Do I need new axle nuts or seals before installing this?

The assembly ships with bearings already packed and sealed, so you don't need to repack anything. You will need fresh axle nuts and cotter pins—grab those from your parts house when you order this knuckle to avoid a second trip.

Can I bolt this straight onto my suspension, or do I need to swap components over?

This is a complete loaded knuckle, so everything stays on it—spindle, bearings, dust shield. Unbolt your old knuckle, bolt this one in. You'll transfer your brake caliper and rotor over, but the steering arm and hub attachment points are identical to factory.

What if my wheel bearing is still good—can I reuse my old spindle?

Not with this assembly. The spindle is integral to the knuckle casting and cannot be separated. If you're trying to save cost, a pressed bearing service at a machine shop might be your path, but this unit comes complete as a matched set.