curious to know if vac suits be able to use in fighters?
Though similar to flight suits when dealing with space (48hrs or 2 days), the large backpack, would that hinder movement or stop pilot from getting into cockpit?

At the moment such suits don't exist but that is probably irelevent to your question.

Vacume suits are designed to be worn in fighters i would imagine and there is no mechanic in place that prevents you from entering any entity due to the cloths you are wearing.

At the moment, nothing suggests that it will not be possible. But an accurate set of rules will be released prior to combat, so it would be best to wait until then, as rules are always liable to change as development continues.

Assuming such a suit was considered an item, I don't see any reason it could not be worn while in a fighter, or anywhere else.