ps4

if i want to play on ps4 do i need to buy the complete collection for ps4. been on pc up til now

Yes, you need everything.

Yes you have to buy everything over

On the plus side it's not expensive believe they just made Heavensward free?

You must buy complete edition or starter edition + stormblood, Heavensward is included. And next, you have to add the license codes in the PSN, you don't need the PS+ (who need sub) to play FFXIV thanks to an agreement between Sony and SE.

And link your current SE account to your PSN account.

If you have PS4 pro think to activate the boost mode of your console that allows you to run FFXIV in High