I was thinking of a USB mouse with a cable that plugs into a USB port, not a wireless mouse with an RF dongle. If I were to use such a mouse, I'd turn Bluetooth off. The question is would a cable-connected USB mouse that got its power via the USB port drain the battery less than a Bluetooth mouse. Thanks.
Each A2DP "service" is Mono-Directional.
A typical device using the A2DP profile for music will not support more than one service (i.e. audio stream), but it's possible. This would need a more complicated chipset so it may not be suitable for the size constraints of "truly wireless" earbuds.
Unfortunately I can't recommend any headphones ...