I've done MDMA redosing with MDA, MDA redosing with MDMA, and also tried some combos like this involving 6-APB. I can't speak to the safety of it, I've mixed MDXX compounds with a variety of unwise agents, but none that were fatal, just things like psychedelics, (meth)amphetamine, NEP, etc.
NEP, amphetamines, and some psychedelics such as the DOx and 25X-NBXX family are likely very dangerous to mix with MD(M)A.
My best redosing strategy so far if only using MDA and MDMA has been to take MDA first, as it lasts longer and comes on within an hour at most. Once it's come on fully, I'll give it a couple hours to really shine before hitting it with the MDMA redoses. I'm almost guaranteed to be mixing a psychedelic such as LSD, 2C-B or miprocin with it though.
Also remember that MDA is stronger per mg than MDMA, so you'll need less MDA for a somewhat equivalent effect.