I'm not divulging anything specific, but my little lady knocked about 20% off a regular session price after about our third session.
When I'm flush, daddy shares the wealth but when things are tight for me and I've had a rough week ... it's nice to have Universal Hottie Care
To answer somewhat specifically:
A- The number of visits varies.
2- I would and do donate less when offered, but I also donate more when I'm flush.
C-SP's do certainly discount their regulars, but I'll tell you that just coming back every week doesn't necessarily a regular make.
An SP shouldn't have to negotiate their fee after the first visit, and if you really like them, you should be discreetly but clearly setting their fee on the table or shelf where they can see it to ease their mind about admin. Wash and shave, and be generous and considerate in your attention toward them. Get yours, but think of their needs as well. SP's also like massages and kind attention, and if she's the kinda girl that would make a good regular, she will appreciate your efforts and want to keep you coming back.
4- I wouldn't ask for a discount. You can try hinting, but I've found that the great girls will notice a great guy, and if you're treating her right, she'll bring it up herself. If she doesn't, and you really need this, then it's decision time for you.