i have some questions about this: 1. will this always work?
In principle, this could be enough. ...
These are complete VM's with Webserver and Postgres. Once per day I take a complete snapshot of everything and feed it in our backup system.
Is this enough to get my Database always up again or do i miss something? Continuous Archiving is not my intention.
Why not try it? Start Postgres running on your backup machine, and see if it works. You should be able to scan through all of your tables with simple "select ..." statements and verify that they're all correct. Then stop Postgres.
One of the nice things about rsync is that it will erase any changes you make to your backup. After you test your backup, it will no longer match your production version. But the next time you run rsync, it will erase all of the changes to your backup and make it match the production version again.