Re: Money $$$$$
I hate to be the evil guy to say this, but you should have agreed on some way for it to be more reliably done (i.e. ask the manager of the company directly and sign something). At this point, balance your books as if you won't get paid, but keep trying. Keep sending emails, keep calling the guy, and perhaps even find a show he's doing and ask him about it while he's there (mean, but gets the point across). The other members probably have better ideas, but it will boil down to: don't expect to be paid. Also, the payment might not have been processed yet by the finance side of the company, since it's been two weeks and they might pay all of their expenses off at once at the end of the month (or a two week pay period- maybe you're on the next one).
About rates... for you as an engineer yourself, I'd say 50 dollars a night for labor, maybe something hourly around minimum wage, maybe higher- but don't go too high. Equipment is much different, and you need to calculate that out for yourself based on how much you paid for it, how many times you think it will last before breaking, how much you need to make to break even as a whole (and the percentages of what you paid for the particular piece compared to the whole rig), what you need to be able to have on hand for repairs/future gear, and finally, how much you like the people you are working for. If you're not the best guy out there right now, shift your margins cheaper, don't charge as much, take tips if they come. A great way to determine the cost for a system is go and build the closest one you can find from an existing rental company, and then try and factor in comparative skill between that owner and yourself.
A system that I'd bring to a 300 person outdoor gig would probably run about 500 dollars including all the extras (cables, effects, microphones), but the barebones for just the core system would probably be about 200-300, but I might be skimping. If you really just want to get out there and do stuff, charge 50 dollars nightly for you, and then tack on gas x2. Simple.
ohhhhmmmmmmmmmmmm *prays to summon people with a better idea of the industry to come and contribute*