don't need to touch anything except the psu. the rest of your rig will keep up fine. that phanteks has official support for up to 340mm long cards without the hard drive cages (you will likely need to remove those), and the EVGA FTW3 3090's were 300mm cards on the dot.
absolutely the fucking do not try to run a hungry 3090 off a 550W CX supply. the infamous 30-series transients will trip that poor thing constantly. buy a 750w or ideally a 850-1000w fully modular unit from SeaSonic, Corsair, or EVGA.