Unless you have a cheap computer it will likely be a downgrade graphically and performance wise, not to mention the psn problems you always hear people complain about. So sticking with PC may be your best bet since you would have to rebuy the entire game.

If you do decide to buy it however, just download it onto your ps4 and then enter your same log in information and it should pull your game up. You will need to redo everything from UI to hotbars to macros to everything so its usually a pain since you will need to constantly update these things on one platform or another as your gearsets and macros change.

Also know that when stormblood comes out will would need to buy both a pc and a ps4 version to have it on both as well.