As to backup, how extensive you go is up to you and, to a large extent, the nature of your photograhy "activity".
I am an amateur/enthusiast. I am not "in the business", and so my photographs are not "business assets". So, my approach to backing up my photos is basic -- I have a dedicated hard drive which has system backups and also has a dedicated backup of all my data files -- photos, music, documents, etc. The drive is unplugged both from power and the computer when I'm not doing backups.
Then, I use an external drive as my "library drive" where all my photos are stored after I have done short-term work on them in my internal "data drive".
So, for my backups, I'm in good shape as far as an occasional power outage/surge or from my computer going crazy and corrupting all my library files.
But, the point gets raised about things like theft, fire, something that could mess up that external backup drive, so a case can be made to have a separate, second backup drive that you back up your stuff to, a mirror of your "regualar" backup drive, and then you move the second drive to a separate location -- a family or friend household, your place of outside work, or even a bank safety deposit box.
And, sure, that is catastrophic "insurance" of your photos, and in that sense it makes sense, I just haven't gotten there.
But, if I was in the business and, like I say, photos were "business assets" then I'd certainly adopt my backup strategy to fully protect those assets.
As far as how your external drives tie into your photo workflow, well, I could say that if you are happy with how things perform, then more power to ya!
But the one consideration there is that as a rule external drives are significantly slower than internal drives. Now in recent years the capabilities of external drives regarding speed have gone up a significant notch. We now have USB 3.0, Firewire 800, and ESATA drives, all of which are becoming increasingly common both in computers that will support them and devices that use them.
So, if your new Mac has one of these bus systems "on board" and you buy the appropriate devices and cable to use these fast busses, then you should be good for, well, a long time with your performance needs.
But, if you have say a USB 2.0 hard drive and you are doing all your processing using that drive, well, you will be taking a performance hit. You say you are happy with your speed and I won't belittle that, but just consider the fact that as your library grows, and if your volume of shooting grows, then your performance will be bottlenecked by that USB 2.0 bus and device.
Now, a limitation is in your Mac. If it only has one internal hard drive, and it is not a high capacity one, well, that is certainly a limitation. I can understand not wanting to put many photos on it, and in fact using your single system drive for a lot of things is not a good idea.
So, it's hard to advise you as to what your "best practice" would be in that case, especially if you are limited to a USB 2.0 bus.
I do have a little cheap laptop with only one internal hard drive. But it's not my "serious" editing workstation. So with the laptop I can play with a shoot, maybe process photos and shoot them up to my Web photo host, but in time, that shoot will if needed and appropriate go onto my workstation internal "data drive" (it's network-shared). On my workstation the internal data drive, separate from my system drive, is where my photo shoots are imported to into Lightroom, and they stay there until I'm done with any short-term work -- editing, keywording, exporting for the Web, printing, are all done from that fast internal drive. It also has resources that can benefit from the speed -- my Lightroom catalog (containing previews) and my Camera Raw Cache, which contains large previews for Lighroom and, if you have it, Photoshop's Camera Raw -- these "live" on my internal drive, as well as my Photoshop Scratch file and other stuff that can benefit from the high performance.
Then, when I'm done with the short-term stuff, I use Lightroom to move the shoots onto my external library drive into a parent folder which is the year for the shoot, and there they wil live -- they have been incorporated into my Lightroom catalog so I can always "see" them and access them in Lightroom. And I do make use of that catalog feature -- I revisit "old" shoots a lot, sometimes just to check one something, but also to revisit editing and such. For that type of thing I'm OK for the slower speed although if needed I can just move the folder back onto my internal drive for the time (I have plenty of disk apace on my internal drive).
Now, all that rambling -- I hope you got some good info and ideas!
Seriously, my husband is taking the iMac in to our computer guy this a.m. to install MS Office & he's goign to get him to reformat the external drives for me. I just can't risk losing any of my sessions I haven't edited yet.
