RE: space hulk basing
if you intend to use them in 40k, definatly. You will want to use the 40mm round bases. (Will make it alot clearer which minis are base to base, make measuring more accurate, etc). Using them without proper bases in 40k would make them look a bit strange on the board and make things a bit ambiguous when playing.
If you want you could make the bases detachable, but they probably wont detract from their use in space hulk games anyway (some people based them for use in space hulk just to make which way they are facing clearer)