Take a look at Pine64 Quartz64 boards as a decent alternative

You're best off using the PROXY protocol assuming your application(s) support it.

This is completely standard for residential ISPs at least in the US. Your options are to either host this elsewhere or use a smarthost (somewhat of a proxy) for outbound mail.

gitlab, several docker containers, kbin, ircds, a bouncer, 3-4 web servers, a couple seperate mysql servers, Handshake DNS hosting and Handshake nodes

Proxmox is all I use for VM hosting, it is well worth it IMO, I colo metal and I host several virtual machines on it, webservers, ircds, kbin, etc. I specifically use Virtual Machines (KVM) however, it does have the ability to do containerization too (LXC).