I believe Storm Lake makes a threaded barrel for the M&P if you can find one.
Suppressors will depend on what you want to do with it. SWR Octane-9, TiRant-9, or Osprey-9 are all the rave these days, it seems.
The Liberty Mystic is a nice can, in that it's versatile and can handle just about anything you care to throw through it.