With a server like that I assume you'd be running VMs, that means you need at least 3 servers for a proper cluster. (only 2 can cause split brain so you wait uneven number)
You'll also want a SAN. May as well throw in a 10 gig switch for iSCSI.
TBH when I get to a point where I have money to throw at newer hardware I'm kind of eyeing Ryzen for servers, it might not be "server grade" but most of the boards for that platform can take 64GB of ram. 3 of those systems would be quite a nice setup compared to my single server with 32GB of ram.
I THINK Ryzen boards might even do ECC but I'm not positive.
I want to play around with Proxmox. When I first tried it it had lot of weird quircks but I'd imagine it's better now.