I try and limit myself to 250-300mg tops in a night. I've tried pushing it over that, and every time the side effects were simply too unpleasant for me to want to try again.
If you want to be high for 8+ hours, try adding a drug like LSD or ketamine into the mix. LSD before a roll will GREATLY extend the length, and ketamine after will make the comedown so amazing you'll almost think you're rolling again. Taking more and more MDMA is never a good idea though.
After a month you'll be back to normal, so to speak.. but you may want to wait a good 45-60 days after such a high dose to REALLY be sure everything is back to the way it should be.