dedicated server and nas in one

Solution
Yes, I have a one computer to perform a multitude of server functions for my home.
For your purposes any dual core computer with 8gb of ram from this decade will be just fine.

In regards to being a NAS:
You can just hook up a bunch of drives and share them individually, or you can use the motherboards built in RAID utility, or you can get an aftermarket raid card. Most motherboards built in support for RAID0/1/10 is adaquete but most are not up to the task of handling parity for RAID 5 or 6 so you would need a dedicated raid card.
Yes, I have a one computer to perform a multitude of server functions for my home.
For your purposes any dual core computer with 8gb of ram from this decade will be just fine.

In regards to being a NAS:
You can just hook up a bunch of drives and share them individually, or you can use the motherboards built in RAID utility, or you can get an aftermarket raid card. Most motherboards built in support for RAID0/1/10 is adaquete but most are not up to the task of handling parity for RAID 5 or 6 so you would need a dedicated raid card.
 
Solution
If you plan on using many drives (like 5 or more). I highly suggest at some point upgrading the case to Fractial Design Define (4 or 5) serries case.
That is what I use and it is a top notch case with good cooling and sound deadining and best of all it holds 8 full size 3.5" drives PLUS 2 2.5" hdd/sdd behind the motherboard tray.