There's a real danger hiding in the 'speed+alcohol then mdma later' combo. The amphetamine masks certain effects of alcohol and it's very easy to drink more than you would need normally. Then if you take a good dose of mdma and the speeds effects begin to subside plus having lots of alcohol in your blood, you might set yourself up for some blackouts and memory problems. I'm not talking about two beers obviously which is nice, has calories for dancing but the amount people usually party with. A beer or something every half an hour with some shots (because you can drink that easily on adderall) and bammm.
I'd proceed as suggested by infectedmushroom, 500mg is a lot. I usually take 120+60mg of uncut mdma a night. If you are not prone to comedowns, go for 120+80+80, that should give you a roll like this(empty stomach):
20-45 mins onset
5-20 mins come up
3,5-5 hrs plateau
1-2 hrs comedown
That's somewhere between 4,5-7 hrs of rolling (result vary from person to person, also set&setting dependent).
Also redosing more than once may increase undesirable side effects and may result in some mood swings the following week. Not everyone is prone to that but we have seen people having bad reactions to it. I am not sure of it but I'd bet this contributes to losing the magic sooner though, so I'll stick to one top-up in the future every now and then while my regular is just one dose of 120mg once a month.