I can't see any reason why not. It's expensive, but it can provide a system to retreat to.

Yes. You'd also be able to fire PDS, if enemy ships are within range.

Just to note, though, you aren't allowed to activate Supernova's or Asteroid Fields, even just to "stall". Not that it's a huge issue (there are plenty of systems you could use), but it can be important as any system you activate in this fashion is obviously "off limits" to you later in the round, so it could be used by another player to move a fleet in without too much fear of reprisal.