1 yes works fine.
2 not 100% sure but I believe it's fine.
3 sound bar on own works but for a more "immersive" experience you can add a pair of play 1's as rears and the wireless sub.
4 I have single 1's in our bed room and a spare for use in garage or kitchen etc and have never felt I'm missing out by not having stereo, I guess its location / use dependent.