So if I've downloaded a mod and then I take the stuff out of whatever that mod gives me, and then I get rid of the mod, will I still have the things or will they dissapear?

It will disappear I believe. I've not played it in a long time but that's what I think will happen. Also remember that if you download mods you can't get trophies.

Yes I knew the trophies thing, I just made a character to test out some mods

That should be ok as long as it's a secondary file. Just remember to make a secondary save for mods.

I just download the mods that give you cool houses or they clean up settlements