Hardware advice

Hi,
new Proxmox install; I want use this installation as "all-in-one" server for the LAN infrastructure.
So I want use a ProxMox box to run:
- a VM mail server (KVM, Debian), (100 GB)
- a Win 2003 VM (migration of current physical that host same legacy applications), (60 GB)
- a CentOS VM (KVM), for testing porpouse (50 GB)

And use the physical host as File Server (Samba) + Domain controller for LAN PCs. (3-4 TB)

Any advice on the hardware?

I am evaluating if it is better a server like IBM x3650 with 6x2 TB SATA HDDs (RAID card), or using an external NAS.

Thanks, P.