choosing a flash modifier

I've been asked by a cousin to be the photographer at her sons communion .. she's offered to pay, however I don't think I'll be accepting any money . I'm no pro and although I like to think that some day I could be a i know I don't have the experience or skill to start charging today .. especially family ..
But as a challenge to myself I'd like to handle this as if I were a pro and I was getting paid (or as close as I can with my limited skills)
She wants portraits done on the 19th of this month and then to cover the ceremony and celebrations afterward on the 9th of may

For the portraits .. which she wants some done out doors and some at church I have a small white umbrella (with stand of course) and my single 430ex flash..it's on a wired connection but I will probably get the yongnuo trigger so i can be wireless and have some freedom..so I think I have just enough to do the out door portrait?

My main concern is at the ceremony and other indoor shots after wards ..
I've been using the cap diffuser thing (excuse the lack of technical terms)that came in the box with the flash pointed upwards..
And while iis better than direct flash pointed aat subject ive been researching other modifiers
I've looked into things like Gary fong light sphere, rogue flash bender and small light boxes .. again all for on camera flash
Again this would be to use for church ceremony and walking around at celebrations afterwards which will be mostly indoors..
or if you think tthere is one ideal for one thing but another for the other I'm open to that as well I'm not neccasarry looking for one item to cover all
Any advice, tips, recommendations would be appreciated

Don't use a flash during the church ceremony. Jack up the ISO to keep your shutter speeds high enough. The 5dIII can take it.

The flashbender is much better than the diffusion dome on the flash- it would allow you to direct light, instead of simply scattering it everywhere (what the dome does). For a cheaper solution, try a rubber band and a white index card.

Alternatively, where are these indoor images going to be? If you have white walls or ceilings, bounce your flash off those. That is the go-to solution for on camera ETTL event flash.

A single flash can't do much if you are outside on a sunny day- it isn't enough light to overpower the sun. Find an outdoor location in the shade and use your flash as fill for the subject. Reflectors also work well on sunny days.

Thanks for the response .. the after ceremony indoor shots will be at a nearby restaurant ..I'm assuming it's not going to be bright lighting as most decent restaurants aren't lit like a mcdonalds?
I should probably make a quick stop there before to know what I'm in for