Those old Dell Rxxx servers will make you poor with the amount of power they use. If you are going to self host, consider a mini pc, you can get one that can easily handle a witness for a couple hundred dollars. If you are determined to host yourself. A typical mini pc is 6W to 20W compared to 200-500W of a Dell server.
This should handle a witness no problem, I have one with 3 VM and 60+ docker containers running in a proxmox cluster and the power is around 11W.
Once the lite node functionality is more officially released, it should be even easier.
Thanks for the info, just ordered this. Do you by chance need 6 new SAS drives? Don't think I can return them now.