I very much doubt that would compromise it

You can lock your signal account with a password/code so that can’t happen

not currently, they do seem to be actively working on adding usernames but who knows how long that will take

what features does olvid have that matrix doesnt have yet?

syncthing is probably one of my favourite FOSS projects its just amazing

https://pterodactyl.io/ here is one I’ve found when I was looking for the same thing, I havent tried it out myself but it looks alright

also https://alternativeto.net/software/pterodactyl/ here is some alternatives if you dont like pterodactyl that much or it doesnt work well