A few questions about a single user instance

I first used lemmy on lemmy.world but due to its size I had several issues of things just not loading and needing a full page refresh. So I tried to set up my own instance and it works mostly but the federation aspect is leaving me with a few questions.

Will remote communities only sync new posts from when I subscribed or will past posts show up eventually?

Is having a single user instance realistic or should I try find another small instance?