The COM port(s) in use are machine specific. They can vary. My laptop usually uses COM40 but is currently using COM7 but it has n ever done that before. The Toshiba handler on my Dell 430 only uses one port. I found it just by blundering through the list.
I don't know anything about uploading Arduino programmes via bluetooth but there is never any obligation to do so. If you can connect the cable, use it.