1. Yes I am using RD-RX800 and FD-8000 with 6800 shifters and crankset
2. SRAM 11-36 is 1x "optimized". I personally use a sunrace CSM8 11-36T. You will need a bigger chain for 52x36
3. Yes the FD8000 is amazing and the tension adjustment screw is much better than fiddling with barrel adjusters. I got one for $33.