Windows edition has the core game and all the DLCs except for Episode Ardyn, which you can buy separately or as part of the Episode Ardyn Complete Edition bundle on Steam. As far as I know there is no meaningful difference between Royal and Windows edition, other than skins and technical stuff (e.g. Windows edition can go up to 120 FPS).
There are 13 achievements in A King's Tale: Final Fantasy XV, worth a total of 1,000 Gamerscore. You can view the full list of A King's Tale: Final Fantasy XV achievements here.Luminous Engine in which Square Enix started developing since 2011 and spent millions on it, made FF XV and abandoned it. FFVII remake started development in the Luminous Engine but it was scrapped half way and development restarted on Unreal 4, which ended up looking a lot better and working better too.