The best would be to have 8 academies until you get enough of their production (I forgot what the hell they were producing
). After that, if you aren't in a big hurry you can manage with 3 sets of factories and 2 vaults (or one vault only because is requested by storyline quest). I did pretty well in my small city with just 2 academies, 2 sets and 1 vault. Went a bit slower but not too slow.