You may need to google A2DP to find out more info about this profile.
For question 1, Yes. As long as they support A2DP profile.
For question 2, I have no idea.
For question 3, currently the sound quality of BT stereo headphone is just so so. IMO, it's a little bit worse than normal mp3+3.5mm headphone.
BTW, personally I use BT headphone because of its following convenience:
1. Most of BT headphone supports AVRCP profile, so you can forward/rewind music tracks easily. This is a big plus for me.
2. In case there's an incoming call, a warning sound will be sent. You can switch to phone by 1 click. So you wont miss a call when listening music.