That is an outstanding job, you honestly could not have done anything better at all there.
Everything is clean and out of the way, there is no airflow obstruction, it looks great and what is more impressive, it looks very tidy from the back too!!
The P4 cable being tight will not matter at all. So long as the cables aren't pulling out and so long as you aren't pulling the port too much, it is fine
Looks fantastic to me, puts my cable management to shame! What case is that you have there?
I don't really see any room for improvement at all, but I think black SATA cables would look nicer. I never liked the red ones that much.