Do I need to remove the mirror housing from the door to install this?

You'll need to pop the housing off to access and seat the glass. The housing itself typically stays attached to the door — you're just swapping the lens inside it.

Will this come with adhesive or clips to hold it in?

The lens comes as-is. Most factory housings have a channel or lip that holds the glass in place once seated. Test-fit first to confirm your housing's mounting method before committing to any adhesive.

What if the glass doesn't seat flush after I install it?

Check the housing for dirt, debris, or damage to the mounting surface. Clean thoroughly and try again. If the housing itself is cracked or warped, the glass won't sit flush — you'd need a replacement housing at that point.