Re: Sims 4, How to back up expansion/stuff Pks.

As long as you turn of automatic updates in Origin (in my experience having them on has undesired sideeffects), you should be able to just download the expansions you want.

Any save games saved with content from packs not installed potentially lead to issues though (for example, having saved the game in Granite Falls and then uninstalling it, might corrupt the save for goo)

The user files are all the same so you can just back that up. The game files don't really need backing up unless your on bad Internet and redownloading is a problem.