I went through a similar process during my search for a practical rifle a couple years back. My criteria were similar, though slightly different. The only modification I ended up making to my rifle was installation of bottom metal to accept a box magazine. It already had a 16" threaded barrel and mounting for conventional optical sight. I added a SilencerCo Omega 30 suppressor and a Trijicon AccuPower LPV sight. Oh and a larger bolt knob.
It was a fun project. So what are you going to do?