I'll read the thread later for amusement, but having read your first few posts.....
What pews to buy is the last question you ask. You're setting up a business ffs. Location, facilties, insurance, staff, marketing.... all of which are probably easiesr to answer than what budget toy is least susceptible to kids, morons, and moronic kids, plus the few beginners that will eventually buy their own and become the l33t like us. Innit.
I've only been doing this a few years, but jeepers talk about going in arse about face. Let alone acting like a total douche canoe with zero sense of humour and skin as thick as McDonald's rice pudding.
If you're planning on running an Airsoft site, you'll have to deal with far worse than you've got here especially if ex military types rock up or the local fuzz decide they want to vent their workday stresses (yes I've played on sites like this).
To touch on what pew....M4, chunky stock battery housing, quick change spring and abrand that has readily available spares, short barrel, iron sights.
Now if you don't mind.... I have several pages of hilarity to read.