It basically boils down to experimentation, what works best for you in your home may not work for me in my home. It is always best to start off with fewer holes so you do not have to tape up holes if you put too many in. I would however, recemmend placing a couple holes near the bottom on opposing sides for some cross-ventilation, so your substrate doesn't grow you some new pets
Not so much a necessity in short and medium cages, but when the enclosures get tall like that, the air won't get a chance to circulate much in the bottom. Even 2-3 holes on two opposing sides can help dramatically, if placed correctly