If you are getting the game on steam keep in mind the last update broke basically all the old mods, and it was late enough after development that they didn’t really get updates. If you want to mod the game or avoid it pestering you about logging into epic use the older version you can apply in the properties of the game in steam.
Also know that if you want to play coop ymmv, its a fun game but crashes and disconnects are common, and your progress with your friend might desync if you disconnect, so you may need to juggle who is hosting.
TLDR: good game, buggy coop, mod scene is sort of complicated due to late stage patches to implement EGS stuff.
I believe the new edition has all the dlc included though I dont know for sure if they’ll work in the old edition, I had already owned the old dlc when the epic update happened. I assume so but I can’t guarantee it. As for content the re elected version is basically just the base game with all the dlc included, so there wasn’t anything new besides jamming epic integration and crossplay into the game.