having cooked for groups from 50 to over 300 and having been a groom on a very small budget, I will just echo the others and say dont do it yourself
to be honest, coming on here asking the kind of questions you asked in the OP gives the impression you dont need to dive off into this yourself
if your friend is gunna do it, make sure he knows what he is doing, like trial runs on the pit(s) he will use for the event
I understand completely the need and want to save the money, and it can be done, just make sure your friend (better if plural) know what they are doing well ahead of time and not 'figuring it out' for the big show
little things going wrong can upset people in ways you probably cant imagine
how much time before the wedding?
how big is your pit? can it handle all you need cooked, or do you need to borrow another or cook ahead of time?
ohh, and congrats on getting hitched