I don't feel as though any of the mechanics are extraneous, but they may need a bit more tying together overall.
I think the breakable glass and depressurization to outer space is an excellent element, as it forces you to be careful about which gun you use to shoot, and from which angle. It reinforces the careful planning element of a stealth game quite well.
A slight addition to aid the player in making informed choices would be being able to see what weapon an enemy is holding. It can be a bit rough to try to surprise someone from behind only to find out they were holding a shotgun.
Also, I found out you can be crushed by closing doors, a nice little detail :3
I generally agree with what v_agdg_feedback said.
Quite a neat game/set-of-mechanics overall, you have a strong base game. I think you should prioritize tightening the controls and providing more environmental cues to the player; stealth games rely on being able to make informed decisions quickly. Keep up the good work, it's looking awesome! :D