Will this glass work with my existing mirror housing bracket?

Yes. This is designed to mount directly to factory mirror housings using the OEM fastener pattern — no drilling or adapter plates needed.

Does the convex curve provide enough visibility at highway speeds?

The optical geometry matches Ford's factory towing mirror spec, so you'll get the same sight line and blind-spot coverage the truck was engineered with.

What comes with this — just the glass, or the whole mirror assembly?

You're getting the glass lens and backing plate. The mirror housing itself stays in place; you're swapping out only the optical element.