I tried just about everything I have been able to find out, but I only managed to get a good ferrotyped print once or twice. Either I get the kind of zits you've got, or (more likely) everything just remains stuck together with no way to get the print off the plate. I've tried stainless steel, plexiglass, regular glass/mirrors and some types of film/foil. So in short, I think I don't really have any useful advice to you, other than perhaps take the easy way out and print on glossy RC paper...not quite like a ferrotyped FB print, but it gets close.
Anyway, I'm interested to read what kind of suggestions you'll get; perhaps I'll try my hand at it one of these days again, if I can muster the courage for it.