Not hetzner but a similar provider:

    - Deploy by stopping the server, rsyncing in the changes, and starting the server. The whole thing is automated by script and takes 5 seconds which is acceptable for us.
    - Run apt upgrade manually biweekly or so.
    - We use client-side load balancing (the client picks an app server at random) but most cloud providers will give you a load balancer IP that transparently does the same thing (not for free though).
    - For scaling just manually rent more servers.
    - For backups we use a cronjob that does the backup and then uploads to MEGA
    - For security we setup a script that runs iptables-restore but this isn't really all that necessary if you don't run anything that listens on the network (except your own server obviously).
    - DDoS is handled transparently by our provider.

While this might change if you're super big and have thousands of servers, in my experience simple is best and "just shell scripts" is the simplest solution to most sysadmin problems.