I stopped using Start9 as a serious node because I mostly manage my nodes remotely. Umbrel has Tailscale VPN, which I use to access all my nodes, but Start9 only uses Tor, which works, but is slow and a pain.

This is why I don't use it in a production server.

As for your spec, I don't think Start9 is demanding on the CPU, but in my experience the more RAM the better.

8GB for any node OS is the minimum these days. I have an Umbrel home, which has 16GB, which is fine as a pure node, but I'd like to run other things on it, but I dare not with only 16GB.

A lot of people highly rate Start9, I'm not certain why. Umbrel definitely has the UI, which I'm a sucker for. I believe many rate Start9 because it is a more robust OS, built from the ground up as a node, whereas Umbrel is an app sitting on top of Linux.

I understand the difference, but personally, I think this point is moot.