The DEA and FDA generally don't seem to go after individuals--lately they seem to be most interested in going after pharmacists and pharmacies. Again, most of my knowledge on their approach to controlled substances has to do with narcotic painkillers, but I imagine it would be similar with stimulants.

If you're really worried about getting into legal trouble, I'd suggest talking to an attorney, if that's possible. (I don't know your financial situation, etc.) I'm not an attorney, but I used to do legal research for one, and law enforcement doesn't generally target individuals like you. Generally, if they're targeting consumers, it will be a big case involving multiple dealers, and it seems very unlikely you'd get unwittingly caught up in one of those cases. You're much more likely just to have trouble getting insurance to cover it, which is annoying but not insurmountable.

And as far as insurance covering meds, when I've switched from one drug to a different drug in the same class, my Medicare/Medicaid has always covered the new drug, even when I'd filled the old one just a few days prior. Granted, these were non-controlled substances for a physical illness, but I imagine it wouldn't be too different with stimulants.