My apologies for not answering this sooner, I only occasionally stop in this forum.
You will want to make sure that your blood mercury is lower than your brain mercury. Otherwise, taking ALA will actually carry it into your brain.
Given your circumstances, I would try to do at least a month of DMSA prior to doing ALA. Andy usually says 3 months, but I believe that is with the assumption that you begin DMSA 4 days after Amalgam removal. I didn't start DMSA until a month after removal, then did 2 months on DMSA alone prior to DMSA/ALA.