I expect this to evolve like email did. It used to be very easy to host your own mail server but due to spam the large providers started using whitelists and nowadays it's almost impossible to have a self hosted mail server that is approved by the others.
Similarly, I expect that hosting your own Lemmy instance will be impossible in the future. We should enjoy it while we can.
Not idea, try asking in the "self hosting" community. The instance im in was created by the mods of the r/brasil subreddit and its works great (for me) because is not as popular as the bigger ones and is hosted locally in Brazil.
The soluition here is to use any other instance then the 3 big ones: lemmy.ml, lemmy.world and bewhaw.org Lemmy instances scale horribly, the more users the worse the performance.
See this piechart from a week ago, the top 3 have over 50% of the users: