Dunno if there is a limit... i once took the 24 hour viagra, but never actually reached the 24 hours of fricking, you pass out before that happens (maybe about 18 in game hours), but never actually died... maybe you need to have bad health and frick till you pass out and then you died...
Regarding how many times u can cum... dunno, my max atm is around 46 i believe, at 76 days, and i stream with death grip until i unload it all on max speed.