It works fine but if you want to OC you should use the 600w psu
Yes but it requires you to cut the chasis where the lower 140 frontal fan could be, also you need to cut a part of the plastic support of the frontal panel, the results are imperceptible and all the panels close perfectly.
I don't have any problem with this configuration, and I play several hours in a session, also tested it with various benchmarking tools for about 1 or 2 hrs.
No, its not possible, the only way to close the back panel is to install the PSU a little up of the radiator of the Kraken, as other users here reported
Have you tried temps for this build with the STRIX fans oriented to the rear panel?