It’s just an old gas cock. Can shut it off with a crescent wrench but are known to leak. If you plan on changing your appliance then call your plumber to change it out, otherwise let it be.
You can get a floor mounted rear discharge toilet easy enough. A true wall mount will require a carrier. The venting and fitting configuration are going to be your biggest issues. Stay away from 90’s!!!
Offsetting the the line is not an issue. Your biggest problems will come when you offset the 3 vertical. The wall will need to be furred out to avoid rolls in the drywall. Also get rid of the fernco fittings on your other 2 verticals.