I still think instances should be largely region based, which is why I started one for Colorado. As far as sharing it I’m not really sure either other than spamming it everywhere (which I also don’t want to do). Instance discovery kind of sucks, you can’t even search on the main join Lemmy page.
Assuming you don’t want to expose these services directly to the internet (I don’t recommend it) then you want to set up a VPN to connect back to your home network. Wireguard or OpenVPN are the most commonly used. As far as guides that will depend where/how you want to run it.
The cheapest CyberPower/APC that is pure sine wave should be just fine.
Lots of cheep SFF/thin client machines on eBay.
If you have open registration you should reduce the account creation rate.