Do I need to remove the entire mirror housing to install this?

No. The glass lens comes out without taking the housing off the door. Carefully pry the lens from the backing plate, swap in the new glass, and reseat it—takes about 10 minutes.

Will this fit my mirror if I've already replaced the housing?

This is OE-style glass for the factory mirror assembly. If you've swapped in an aftermarket housing, test-fit first—non-OEM housings sometimes use different lens mounting points.

Does this come with the gasket or adhesive strips?

The glass lens assembly ships as-is. Most original housings still have a usable gasket; if yours is dried out or missing, pick up a mirror gasket kit separately to ensure a tight seal.