Gunxpatriot - your not an idiot, but you might be crazy, lol
All kidding aside - I was probably one of the first owners of an M&P15 Sport in my area. I picked mine up for $599! My thought's were, "It's a Smith and Wesson, if anything is wrong with it, they will fix it!" Well I was wrong...they don't need to fix it, it is an awesome gun! Accurate and zero problems!
To answer your question...
DI VS Piston Driven - people will argue for either one until they turn blue. On a lower priced AR15 - your only choice is DI. If you up the price - then it's up to you how you would like to spend your money, because I think both systems work.
Lack of forward assist? I've yet to use the FA in a shooting situation whether local range or military. Only time I use it is in the classroom.
Sorry - can't answer third question. I'm in MS and we don't have the same rules.