I don't have a bank of pins in the main room because of the way the room is laid out, and people tend to play more in there because they've got room to breathe and someone can stand beside the pin and watch someone else playing. In my second pin room I've got 3 lined up on one wall, and there is about 2" between the heads. It is fine with 1-2 people playing, but can get really crowded with more people, and is a pain when trying to work on the playfields.

I'm normally all for cramming in as many as possible, but just make sure you are comfortable with the space between to be able to get to the backbox or access the back of the playfield if need be. And sliders are your friend. All mine are on hardwood with sliders so I can move them around if need be.