can maps operate over bluetooth

If your car supports wireless Apple Car Play it will operate over Bluetooth only. That's how it works.

That does not mean however, that your iPhone will not use cellular data to download the maps and calculate routes because it will.

The connection between the iPhone and the Car's head unit / media center does not have any bearing on how your iPhone uses maps.

The Map data will still have to be downloaded through cellular data. The information transfer between the iPhone and the car does not in itself use any cellular data wether its done through USB or Bluetooth.

That depends on the specific model car. Some can use Bluetooth for maps, but other require a USB cable. Check your car’s manual.

Then give it a try and see how it works.