digitallyfree
The boost also apparently sends the post out to your subscribers, whereas the upvote does not.
The pinnacle would probably be a dedicated Ampere server or workstation.
How would you compare it to Matrix? I use Matrix and have never tried XMPP.
Yeah personally I'm not a fan and I would rather follow a well-written guide than spend even more time auditing such a script (which would be even more difficult if you're not experienced with Proxmox). For maintenance's sake it's also risky getting your service set up like this as you don't know how the script set things up and it's harder to fix things if they go wrong.
I've never used a colo before; my rack servers live happily in my basement. If you google say "1U network colo <city name>" you'll find many providers.