You would have been in for a ride had it just been a run-of-the-mill used MB with that many miles on it. If you're really buying a car that's already been messed with and blown up once, I'd say you're in for a heartbreak.
Used high-end MB's aren't for the faint of heart or the shallow pocketed among us. It takes bucks to start fixing those things when they break, and they are going to break. I wish you the best of luck.
Cruising around the net, found this, if you haven't, you might want to bookmark it. Looks like a great list of common problems and fixes, could be very handy.
https://mbworld.org/forums/w212-amg/721159-looking-t-purchasing-2014-e63-4matic.html