all looks fine, you could get away with the HX520 instead of the HX620 though
Keep the HX620 unless you want to save a few quid. I had the option also and opted for the bigger PSU as you never know what you'll add to the system that might need it.
Rest of the system is looking great, I'm certainly enjoying my gaming at the moment
. Not sure about the P35 boards with no experience with them but I doubt it should have any major problems but maybe best waiting on someone's advice that knows something about the board or have you seen some reviews at least.
good luck, give yourself time,room and decent lighting when you're set too start the build.
as already mentioned really, just take ya time, check the mobo stands are set into the case and match the mobo, double check all connections.
most of all have fun![]()