I like my magpul BUIS, for the optics look at the Vortex Strike-fire 2, you can pick them up for sub $200 and they have a life time warranty to include fire. For the trigger that is all on the person firing it, I like a nice 2 stage trigger but to be honest a stock Colt 6920 trigger is ok. I would get a mil spec heavy buffer, tube, and stock over a commercial one, but that is just me. Post some pic when you get it done, and good luck with the parts search!