You'll be fine. Bunch of my friends were doing just this (+LSD) for String Cheese Incident a few weeks ago. They took 50+mg vyvanse and at least .2 of crystal MDMA (as well as the 2-3 doses + washout from a vial).
If you have a history of heart issues I wouldn't recommend it, as they'll cause a synergy between the speedy side effects. I do however like that amphetamines in this form last longer than the MDMA high, so I'd usually take the amphet a bit into the molly or when coming down allowing me to "rage all night" so to say.