Yeah... wrong forum..
Anyhow, I'll move this, after saying this:
1. no amount is safe, its a damn street drug, and as much as I like it - there is no safety factor.
2. the LD50 (Lethal dose for 50% of test subjects) of MDMA is 106mg/kg oral.
3. no two pills are exactly alike, so keeping that in mind, you'll require a different amount of pills for each batch.
I would strongly suggest registering, and asking questions, looking around for other topics etc.
TheGamer