There are studies in the 50's and 60's looking directly at combining t3 & dexedrine (Dextroamphetamine) but unfortunately they aren't available to the public. But the fact that dextroamphetamine is in the same family as ephedrine, and one of the main ingredients in adderall, I would think the same rules apply.
To use ephedrine as an example, it tends to work better with t3 because t3 upregulates beta receptor sensitivity and ephedrine (stims in general really) increase thyroid conversion. They seem to work in synergy but I would be cautious because stims seem to hit "harder" when combined with t3.
I don't see any need to use more than 25-50 mcg of t3, starting on the lower side of that. As for dosing dexedrine to maximise the thermogenic benefits, I think this will need to be a "start low and see how you react" approach I'm afraid.
Also, I wonder whether these drugs have some kind of catabolic effect aside from their negative effect on appetite.
Ephedrine certainly has anti-catabolic effects because it increases the release of fat from the cells into the bloodstream, thereby increasing the availability of fat to be used for energy by the body, and logically sparing muscle in the process.
Edit: In my haste to provide useful info, I've only just realised that the OP is probably not around anymore lol. Oh well, hopefully someone else will find this info useful