For Synchthing I'd definitely recommend using the 'SyncTrayzor' GUI on the downloads page ( https://syncthing.net/downloads/ ) as it makes the setup a whole lot easier. It's been a while since I set it all up but I don't remember any major difficulties or gotchas. You can choose which directories are synced to each machine, and whether it is bi-dierctional or just a 'backup'. e.g. I use bi-directional synch for Keepass but only one-way backup my camera directory from my phone (using the Syncthing android app) to my home pc/server.
The thing to remember about synchronising Keepass database/files across multiple machines is that each machine has its own local copy and Keepass itself doesn't reload/refresh the file automatically on the other machines. So once you add/update an entry on one machine you may need to go into Keepass and manually synchronise (or it should prompt you next time you update/save something on the other machine). There is a 'proper' way to set up multi-machine synchronisation using triggers ( https://keepass.info/help/kb/trigger_examples.html ) but I haven't set that up.