It depends on your goal. If your server is just a tool you use, you can ignore lot of concepts. There is no local timeline, there are no users, all follows belong to a single user, etc.

I can't find the link but a while back there was a post on the front page about how to get a findable, read only ActivityPub profile by just uploading some static JSON files. Not exactly a Twitter competitor, but you don't need much to start exchanging messages.