If I were to self host, a Mastodon/Pleroma/Misskey with federation turned off seems better choice?

Honk may be a better choice for something like this if you want to use a Fedi base: https://humungus.tedunangst.com/r/honk

It’s already fairly antisocial by design, but if you disable fetching replies it can be a lightweight standalone microblog.

Demo: https://honk.tedunangst.com/