I used to have a serious hoarding problem on AC. I started selling everything that's reorderable, whether it's DLC or not. I have 3 characters in my NL town: Mayor Lainey, Janitor Chris, & Storage Michele. Lainey's house changes a lot so she only keeps what I know I'm going to use daily. Janitor Chris' house has special furniture that can't be reordered or is super hard to get during an event, like the Mush set or the Pave set or the Sloppy set. You're never guaranteed a full set, so I just keep those in his house. He also holds the few male Gracie clothes that I like, & all the extra Sahara walls/floors. Storage Michele holds all the non-reorderable DLC & special items.
I'm starting to go through the storage house & sell off items that I have too many of or just don't need. I only keep 2 of an item for decoration purposes & most of the items are from events that repeat every year. If it's coming back, why keep extra junk that takes up space?