Do I need a new wheel speed sensor too, or is it already on this assembly?

The ABS sensor is already mounted on this assembly, so you're not buying parts piecemeal. Just pull the old hub out, drop this one in, and plug the sensor connector back in.

What fasteners or bolts do I need to install this?

You'll need your vehicle's factory hardware — caliper bolts, hub bolts, and brake line clips if applicable. The assembly itself comes ready; you're just swapping it onto your existing spindle or rear axle.

Will this work if my original bearing is shot but the hub flange looks okay?

This is a complete unit, so you're replacing the whole thing at once. If your old hub is damaged, cracked, or the bearing is grinding, this assembly handles both problems in one swap — no mixing old and new parts.