Really quick:

When trying to kill a centurion on Boarding Party track, do I have to kill the first one or the last one (the one close to the end making cylons to win)? Can I choose what centurion I will kill?

You can choose either one. Choosing any but the closest to the "humans lose" space is silly.

Could have some merit if done by infiltrator, but I would have to be convinced of that.