At the moment I run a iptables rule which restricts the connection count to port 9001 (OR port) to 1000.
If your setup can not handle at least 6k concurrent connections, I'm afraid it is not suitable for a tor non-exit relay.
If you can, run the latest tor source code from git master, it includes important denial of service mitigations that will reduce the load on your relay.
https://twitter.com/nusenu_/status/958486010563874817 https://lists.torproject.org/pipermail/tor-relays/2018-January/014357.html