You won't know how much to take off the pistons, if any, until you have the short block assembled and can measure protrusion, and measure valve recession in your head. Sure you could just take enough off to where you know you'll be safe, but why take off more than whats necessary and lower compression even more? Your quite a bit lower with the large bowl pistons already. Running a thicker head gasket is fine too, it will just lower your compression ratio a bit more. On my last build I ended up having to sink the valves to about .060" and run a .010"+ thicker head gasket. My block had been decked .006" and my head resurfaced .003". My pistons were already coated so I didn't want to fly cut them.
Make sure you degree your cam. I had to change keyways on mine to get it where it needed to be.
I have the Fass 220 on mine and it never drops below 45psi. It idles at 65psi. My P7100 is dual fed. Make sure your return line is not kinked in any way. I only used the pump in the whole kit. The mounting brackets were worthless so I made my own. I have a Beans sump on the tank and a Vulcan drawstraw bulkhead as my return. Nothing factory left in the fuel system. Its more than whats needed for the power level i'm at but I wont need to upgrade later on.