yes this tv can be mounted on the wall i have the exact same tv mounted on my wall i love it just very heavy since im a small person to lift this tv up on the wall
I'm afraid you won't be able to stream Spotify from phone, as Vizio currently doesn't have Spotify app for its TV. However you can stream Youtube from your phone.
Think the Visio M and E series 50" should just fit by a fraction with a inch left over. A Samsung 46" 6030 with 3D will definitely work and leave an inch or so to spare each side (It's ~42+ inches wide).. See my review on Vizio M501 for more info.