As Zanaku said, the PS4 version is free for PS3 players. You upgrade your PS3 account to the PS4 version, but if you do you can not log into the PS3 version anymore (unless of course you purchase another copy of the game I assume).

As for the game version, for FFXIV at least the "disc version" and "downloadable version" are exactly the same (I never heard of one having lower textures than the other for any PS3 DL/Disc game). There are no differences in texture or rendering resolution between the different distributed versions of a game on the same console. A disc version of a game will run the same as a digital version, albeit with longer loading times. Not sure where you heard

The PS4 version will be 1080p of course, all the games on the system are. It will look like it's running on a mid-high range PC I think (it pretty much is).