You bring up a couple issues that get discussed often on the forum.

Different species can be housed together as long as the same size, same sex rule is followed.
With the exception being T.elegans.vagrans (Wandering Garter snake) They can be cannibalistic.

I do a 90 day quarantine period. Here's a link to a thread discussing the quarantine issue.
http://www.thamnophis.com/forum/husb...lk-thread.html