Will this plug directly into my existing wiring harness?

The assembly is designed to mount at factory points, but confirm electrical connector compatibility with your vehicle before installation. If the plug doesn't match, you may need an adapter harness.

Do I need to order the left mirror separately?

Yes. This is a right-side assembly only. You'll need to source the left mirror separately if you're replacing both sides.

How long does the heater take to warm up in freezing temps?

Warm-up time depends on your mirror's wattage and ambient conditions. Refer to your vehicle's owner's manual for heater performance specs on this model year.