How exciting! I put a proposal together for the local Community Classes but they don't see a need yet

Hopefully one day I'll get a phone call to offer it!
Here's how I would do it
Have people sign up and pay a specified amount so that you buy all the materials. I would only offer the one item for the class, everyone does the one thing (in your case pockets), same colour PUL & microfleece and all

Remember it's
concepts you're teaching - the fitted lady can do the same thing at home with fabrics to make fitteds - you're just teaching her the steps KWIM?
If you have 4 possibles, you might be able to offer 2 PUL colours but then 7 might want the same colour

(I actually think that 6 in the class would be about right, 10 you might be a little busy, not to mention needing space to house the tables, machines, etc). Are people bringing their machines or using yours? You'll need to consider things like tables, chairs, power points, extension cords, multi boards.
Do you have a limited time frame? If you do: cut the fabric up into nappy cuts, premeasure the elastic for each nappy for them to work with, count out the snaps, or premeasure velcro etc. and give it to them in a wee kit. Provide multiple patterns (maybe one in each kit) to trace from to speed up the cutting out process (which can be very slow). I would also provide "made up" nappies show each of the steps.
I wouldn't bother with inserts - they can stuff it with a folded flat nappy

Most people have them - even sposie users
I would personally encourage snaps - but I reckon I could get away with that because there are so many presses here in Chc that if someone wanted to make lots of nappies there would be plenty of presses to access (including one at Bumbles). However, if the ladies you're working with are from all over the show, that may not be so convenient - in which case yes, I'd use velcro.
Make sure you have some pens for tracing (or have people bring their own).
Depending on the time you have available, you might not have the time to demonstrate each step (but I wouldn't count on it). Hopefully the range of skills will be there so that a lady or two catch on really quickly and zip ahead, then can show some others what to do. (or at least that's my style).
Gosh, I'm really excited for you! What an awesome project to have!
Good luck!