As long as you are using a DPP or Hybrid dish, yes, it should be plug and play. If you are on a really old installation that uses DP or legacy equipment then you will be limited to one tuner. You can check your satellite dish model on system info (Menu > 6 > 1 > 3), and then look at the box labeled H.
Not sure what you mean here, if you are talking about watching something then changing to the secondary tuner that is recording in the background then yes, this can be done by pressing input on the remote while it is in SAT mode. Also worth mentioning, even though the Wally has two tuners it cannot operate two TVs independently like your current 722k can, it only has a single TV output. You can get creative and split said output to multiple TVs (similar to your 722’s “single” mode). Not a problem if all you want it to do is serve one TV while a different show records in the background.