Not much point in worrying about getting a "top-mount" PSU since an ATX PSU is an ATX PSU regardless of where it is mounted except that bottom-mounting tends to require longer cables.
Not much point in worrying about the 4-pin CPU power connection either since most PSUs either have a 4+4 EPS12V connector or separate 4/4+4 cables. Either way, they should both work.
As for the GPU, you didn't say what it was and unless you tossed a high-end GPU in there, it should not require that much power and run fine with a 6-pin PCIe power connection. High-power cards usually have a combination of 6pin + 8pin connection that allows people to use 2x6 or 1x8 cables.