Will the power and signal functions work right away when I bolt this on?

Power and signal will work if your Mazda 3 already has the wiring harness routed to the door — they bolt to factory connection points. If your vehicle originally came without BSD, you'll need to route the BSD connector to the control module under the dash; the harness comes with the mirror, but installation varies by trim level.

Do I need new glass or is the whole mirror assembly included?

This is the complete assembly — glass, housing, motor, signal module, and all internals. No separate parts needed; it's a straight bolt-in replacement.

What condition is the mirror in, and will I need to repaint or refinish it?

These are OEM pulls in good used condition with typical wear; most retain their factory paint finish. Check the photos for color match and surface condition before ordering. Minor touch-up paint may be needed if there are scuffs, but the structure is solid.