Hi Scott,
Good advice so far, but I think you might explore some other options.
First, look into renting studio lighting. The SB-200 and Fong attachment really won't cut it for the "formal" shots. Pro shops in many cities have at least basic lighting kits available to rent. If you don't know of any in your area, call any local pro shooters... They will likely know who offers rentals.
If you go the rental route, you will need at least two lights (three if you need to light a background) with either umbrellas or softboxes, stands and a flash meter. Also, be sure to rent the stuff for a couple days in advance and practice using it, so you can set up quickly and feel comfortable doing the job when the time comes. The rental shop can probably give you a quick lesson how to use the equipment, but you really should practice with it a little.
You might research basic studio lighting, to get a good idea how it works. You can probably find a lot of info online, or perhaps some books in the library or off of Amazon.com, etc. Keep it simple, though. And, check your camera manual. Likely you will need to use a slower sync speed with studio strobes, than you are able to use with portable flash. A friend of mine uses D200/D300 and we have done some shoots with my location lighting kit where we both used 1/160 without any problems, although both our cameras flash sync is 1/250.
Next, talk some more to your company. For one, in most cases like this the company might pay for a "commemorative shot" of each couple. Beyond that, you might have some additional sales, but I wouldn't count on much. The best way to make additional sales is on the spot, with on site printing and an assistant. But, that's involved and costly.
You might also do some walk-around/candid shots during the event. You can post all the shots online for people to visit and view after the fact But, honestly, if you don't do on-site printing and sales you miss all the "impulse buyers" and will likely only see a smattering of sales online. Still, if you aspire to shoot events, you need to learn to do this. You will need to have your online gallery set up in advance, so that you can print up business cards to hand out. Also try to get everyones' email address, so you can send out notifications of the images being posted.
Be sure to get shots of any awards being handed out and handshakes, too. For walk-around/candid shots and any award presentations, you will need your portable flash (best if used on a flash bracket off-camera, and don't try bouncing if the ceiling is high or any dark or odd color).
The company might also want a commemorative album of the event. Or, they might want you to make some enlargements and post them somewhere to share in the offices. Or, they might want to license some of your photos for use in an annual report, or for use on their website, or to send out with press releases, or for other promotional purposes These would be extras you could charge something for, if you can come to an agreemen.
And, the company might be able to help out in terms of the backdrop. Many have a banner and/or booth used at trade shows, which might be useful at the event. Also scout the location, there may be an ideal set up. If it's a hotel or restaurant, you need to talk to them anyway, well in advance, to arrange setting up and getting access to electricity, etc.
I have to disagree with Suzie about the need for a 5D and an 85/1.2L. Those might be the ideal tools for the job, but you can do a darned good job with just about any of the recent D-SLRs... In the right hands, any digital Rebel or D40 would be quite capable. Most likely, you will be printing 5x7 or 8x10 photos. Even a 6MP camera can handle that.
Lenses are more important than the camera. But, again, you don't have to break the bank. Personally I prefer to use primes for this type of shooting, and for a crop sensor camera like yours, I prefer to use 50/1.4 and 85/1.8 for most portraiture, and occasionally 28/1.8 for group shots. At times I use 24-70/2.8. In part, what you use will be dictated by how much room you have to work. You do have to avoid wider lenses and longer teles, both of which can cause unattractive exaggeration effects in portraits (especially wide angles used too close).
A couple other things:
How will you get the printing done? You might just look for local low cost source, depending upon the company's expectations (and willingness to foot the bill). Or, you might use an online source yourself, have the batch sent to you, then package and resend them to the participants.
For this you might want to buy presentation folders/mats for the prints, and may need envelopes to ship with as well. Plus there is the cost of postage to consider. However, you also might be able to distribute the finished images at work (or get the company to mail them out).
It it's a large company, and there are a lot of people you don't know, one suggestion is to get a list of attendees and write image file numbers next to each one when you shoot them. Another is to use a small white board with dry markers and write their names on that, then do a quick "mug shot" with them to help you recognize them in the images later on.
Now, presumably you want to make some modest profit off any online print sales. That might mean setting up a "pro" account, or whatever they call it, someplace like SmugMug, Printroom.com, etc. I don't know what it costs on SmugMug, but my Printroom account costs me $99 a year.
Finally, coordinate with the company on one more thing. They will likely have a "reception" table at the entry. Make sure that the people working there are told to direct everyone your way, to insure that everyone is photographed. Some will balk and be reluctant, it's up to you to make it fun and "painless". Take several shots of each couple, more only if they want it. Be prepared to take shots of two or three couples, who want a larger "group" shot.
My experiences with this sort of thing are that you can expect relatively few sales to the participants. The only way to make any money on it is to get the company to pay a set fee for the job. That would be determined by how many couples you will be shooting, total, times so much per 5x7 (one print per couple to be provided, at no charge, by the company), plus the cost of rental equipment.
Now, to be even more brutally honest about it, in today's economy many companies are cutting out all costs of exactly this sort. If they were to ask me to shoot it "speculatively", no up front agreed fees and based upon sales to the participants only, I'd probably turn the job down. I suspect there just wouldn't be enough sales to participants to make it worth my while.
Personally I will only take on a "speculative" shoot that's predicated upon sales to the participants as a key source of revenues if there is some after-market potential for the images, such as fine art or stock sales. There simply aren't many opportunities to "leverage" the work from most company parties like this. But, you might want to tackle it anyway "for the experience".
I use a pair of Canon 30Ds and a 10D as backup (a pair of EOS3s for film don't see much use any more), lenses I use most for this sort of thing are noted above (I have a number of others for other purposes), three 550EX strobes with a compact battery pack to speed up recycling for this sort of thing (I have others for other purposes).
My location lighting kit consists of five Norman 320ws monolights, two 60" convertible umbrellas, three 45" convertible umbrellas, several Photoflex light stands and one JTL boom stand, a 10 foot wide Savage backdrop system with several rolls of seamless parper and clotn, and two Minolta incidence flash meters (very important!), lots of extension cords, gaffer tape, "lint/pet hair" rollers, extra flash tubes, spare modeling lights, fuses, batteries, etc. etc.
Believe it or not, it all fits into one, big (heavy!) roller case, except for the JTL boom which has it's own separate bag.
Most often I set up two of the lights pointed into one of the big umbrellas as my main light (using a bracket I made to allow the double setup), one pointed into the other big umbrella as my fill light. I have the option with these umbrellas to use them as "shoot through" diffusers instead, turning the lights around and pointing them at the subjects instead. This I will do when I need more power, due to larger area of coverage or larger groups to shoot.
The boom gets a fourth monolight on it, mounted high above and behind the subjects to illuminate the backdrop. Depending upon what's back there, and how far away from the subjects it is, I'll set that up with barn doors and/or a light grid, or a small umbrella or even a shoot-through umbrella. It can serve to both illuminate the backdrop and as a hair light, depending upon what effect is needed. Getting the light on the boom right is one of the trickier parts of this lighting setup. But, without it the two lights from in front of the subjects can cast heavy shadows. That's especially important if the background is light colored, of course.
I also have a few simple flashes, a couple old Sunpaks 333 and Vivitar 285s and 2500s. These can be set up low and behind the subjects, if needed, with a simple "peanut" slave.
Another little trick... Usually I try to keep the lights close enough to the subject I can set them to half or even 1/4 power. That's one reason I ganged two into one umbrella. By setting all the lights to partial output, they recycle a lot faster.
Radio triggering would be ideal, but I still use a sync cord to one of the strobes, the others are set as optical slaves. Oh, and if you use a sync cord, be sure to have spares on hand. I spent the money for a much better one from Paramount Cords, but have probably a half dozen extras "just in case". I don't know why, but sync cords seem to be the first thing to cause problems with a lighting setup. Still, I'd need 5 or 6 radio transceivers and haven't been able to justify the extra cost... I simply don't do all that much location shooting with this setup.
Using a sync cord and optical slaves only gets me in trouble occasionally. At a recent event someone repeatedly grabbed shots over my shoulder (Dammit I hate that!) and her flash kept firing all my slaved monolights. She had a real knack for firing just as I was pressing the shutter release, so I got more than a few shots where all my slaved lights were mis-timed or hadn't fully recycled. I finally asked her to knock it off and she did.
A final suggestion. Get there early and set up. Test everything. Then mark with tape on the floor where you want people to stand. This way it's just a matter of getting them posed a little, and taking your shots. Quick and efficient. They'll be more cooperative that way.
At this point, I think you mostly need to explore your options with rentals, talk some more with the company to see what they want and how you might get compensated and go scout the location. Once you have determined more exactly what's wanted and what you will need to rent, order and buy, you will be in a position to put together a written quote and a contract with the company. Since it sounds like you aspire to shoot professionally, the sooner you get used to doing this, the better.
Hope this helps!
Get the pp and workflow down, after you practice and then decide if you're in it for big bucks or helping people out. A sheet to print is about $2 for me, and I charge $12/page for senior shots, which covers my costs, that's it. I think you can start there.
