the warning can be ignored. Your old world should open fine.
if you pick up an item, and it is a *CRAFTING* item, you may learn recipes for it. I noted that one thing I picked up was both a food and a seed, and it didn't acknowledge its seedliness (recipe to grow it) until I also had the cultivator in hand. So there may be some bugs with that. But regardless, if you have in hand all the materials to make something, it unlocks the recipe for you, or should. You may need to pick them all up at once, or check the craft station to see if you knew it and already have it marked, whatever, but nothing much has changed here.
Old worlds may not spawn in new content correctly and may reset terrain edits. Old worlds under the influence of mods may be completely broken. But assuming you didn't use mods and don't care about new content, you can go there and tear up your old stuff and bring it into a new world to rebuild; Ive done this and it works fine.