I am far from an expert (but then, neither were you at the time) but I worry about the part where you said you put on a "heavy" coat and followed it up with "5 more" coats. That seems to be a bit of overkill and would then go back to the concerns of heating up and peeling.
Hey, other than that, I think you did a heck of a job and it took a lot of "guts" to do that. Kinda like "going where no man has gone before". Or maybe is should read, "painting where no man has painted before".
Being a perfectionist kinda person that I sometimes am, the only thing I think I may have done differently would have been to take a brand new plastic "scrubby" (you know, the 3M kind for washing really dirty pots) and gently rubbing it on all the spots on the MB I hadn't covered with tape. This would be just to (hopefully) help the paint adhere better in the case of overheating a bit. The other concern would be, as mentioned, the "heavy" coat of paint followed by 5 more. I don't think that was needed. I'm pretty sure that the paint you chose would have done almost the exact same thing, even if you had only put on a couple of light coats.
Trust me, this is not being critical; I think you did one heck of a job and have more guts to do this than most of us here on AT. I applaud you for that. My suggestions were merely that; suggestions.
Great Mod!