Does the fireplace actually heat the room?

It is an electric fireplace, so it produces supplemental heat for the immediate area rather than warming a whole house. Treat it as a zone heater and ambiance feature, not a replacement for central heating.

Does it need to be plugged in?

Yes. The fireplace runs on standard household power, so you need an outlet near the head of the bed. Plan the layout before assembly, because the cord limits where the bed can sit.

What size mattress does it take?

It is a queen bed, so it takes a standard queen mattress. Check the mattress height against the headboard if you want the fireplace visible above the pillows.

How much room does it need?

The frame is roughly 89.5 inches long and 67.75 inches wide, so measure your space with walking room on both sides. It suits a large primary bedroom better than a small guest room.

Is the upholstery real leather?

No. It is a fabric-upholstered wood frame in black. Fabric is softer and warmer than leather but stains more easily, so consider a fabric protector.

Can the flame run without heat?

Most electric fireplaces of this type allow flame-only operation, which is useful in summer. Confirm the control layout on the unit before you buy if that matters to you.