Absolutely no pay nor any tips for assisting.  I usually supply cookies, soft drinks, snacks, and spare parts for classes.  I like to be able to fix any problem with gear with zip ties, O rings, or string.  I carry a complete tool kit and spare regs.  
I fill tanks, sometimes as many as 25 tanks, if I have time.
Shop gets me gear at cost.  This year, I'm asking for new gear on a "key man" deal, less than cost, because the manufacturer or distributer kicks in a discount on top of the shop discount, so you "show off" their gear. Limited to one set of gear, I think.  Cost is about 50% of retail, except on tanks, which are not discounted much because shops make very little on tanks.
No other DM at our shop gets this deal on gear, because I work my butt off for nothing.  One other guy used to, but got caught up in flying airplanes and isn't around much anymore.  I could probably talk the shop into paying me a small hourly salary for the work I do and use the money to pay for gear and get a better deal.
As far as requirements, you have to pass some written tests on modules, you have to assist a certain number of classes in the pool, and a certain number of classes in the lake.  You have to map a dive site.  You have to demonstrate some rescue skills, and simulated emergencies.  When you get the book, it lists the requirements pretty clearly, there's a lot of stuff.
D
I don't get a discount on trips, but if a trip gets enough customers to need another leader, I might get a free trip someday.  I have gotten two free trips on the Flower Gardens by acting as a DM.
I will be given several PADI specialties free, which the instructor came up with because he took so long to get my card.  Free specialties  wasn't a big deal to me, but it seemed to be to him
and it made him feel good, so I told him I really appreciated it, which I do, because of the gesture.
So, if you're in it for the money, get a job at Micky-Ds instead.