Will this plug directly into my factory mirror connectors?

Yes. This is a direct OEM replacement, so the electrical connector and mounting interface match factory specifications. Swap it in where your old mirror was.

Is the mirror glass heated on arrival, or does it need activation?

The heating element is built in. Once installed and powered, it operates through your vehicle's factory climate controls—no separate switch needed.

Can I use just the driver's side, or do I need both mirrors?

You can replace the driver's side alone. The passenger mirror is listed separately if you decide to refresh both sides later.