If it is just PiHole, you can basically get the weakest computer you can find.
If you want lots of storage space, you will need to make sure you have a case and motherboard that will accommodate the drives.
If you are running encryption on those drives as well, you will need a CPU more powerful than what comes in a Pi, but nothing crazy.
If you are running lots and lots of VMs, you will want lots of RAM. A linux VM will use maybe a few GB each depending on what software each is running internally, a windows vm will use a bit more.
If you are doing AI workloads, you will need a graphics card.
What are you intending to run on this server?
If it is just PiHole, you can basically get the weakest computer you can find.
If you want lots of storage space, you will need to make sure you have a case and motherboard that will accommodate the drives.
If you are running encryption on those drives as well, you will need a CPU more powerful than what comes in a Pi, but nothing crazy.
If you are running lots and lots of VMs, you will want lots of RAM. A linux VM will use maybe a few GB each depending on what software each is running internally, a windows vm will use a bit more.
If you are doing AI workloads, you will need a graphics card.