From a guy who has a storage unit (it's main purpose ain't pins though, although it has some...), I wouldn't suggest doing the storage unit thing unless you can get a really cheap rate, and it is easy for you to move machines in and out of your house by yourself. Otherwise, you'll end up paying a significant amount of money for the storage area that you could instead be putting toward building onto the house or doing something to fit your collection more, if that is your thing.

The best would be if you could find a warehouse or something that would allow you to set up your machines and actually play some of them somewhere else.

I also like (*gasp*) loaning a machine or two out to operator friends to route. They return them to me in better shape then they get them in, and it allows me to yearly rotate the herd... while also getting a whole new set of legit high scores on my machines that I need to beat!