One of the things that you need to consider with housing is how many snakes you intend to keep. If you are only thinking about 2, one aquarium apiece is easier. However, if you are planning on keeping lots of snakes, housing them together is not a bad idea. Alan Francis has good information on this subject too.
http://www.gartersnake.co.uk/maintenance.htm
The only thing I would say is pay attention to what just about everyone says that when you house ccollectively, feed separately. This doesn't have to be expensive, as a plastic container that maybe you wouldn't want as primary display can make a great feeding container.