1. Don’t bother with disabling icmp. You’ll use it way more then it’s worth disabling, and something like nmap -Pn -p- X.X.X.0/24 will find all your servers anyways (same can be said for ssh and port 22. But moving that does stop some bots)

2. As long as i go out not exposing anything the the global internet, you really don’t need a lot. The fire wall should already deny all inbound traffic.

The next step is monitoring. It's one thing to think your stuff is safe and locked down. It's another thing to know your stuff is safe. Something like Observium, Nagios, Zabbix, or otherwise is a great way to make sure everything stays up, as well as having insights into what everything it doing. Even Uptime Kuma is a good test. Then something like Wazuh to watch for security events and OpenVAS or Nessus, to look holes. I'd even though in CrowdSec for host based virus detection. (Warning, this will quickly send you down the rabbit hole of being a SOC analyst for your own home)