The upgrade campaign ended a long time ago, so you'd need yet another new copy. I believe you can probably get a bundle of ARR+HW though for just a bit more than what HW would cost by itself.

The PS4's hardware should be fine. Some people remove the hard drive and replace it with a solid state drive to reduce load times, but the upgrade is rather expensive for a modest performance boost. It's not really necessary for either speed or capacity (especially capacity as you'll have no issues there at all).