Rather than purchasing additional hardware, I’d use the “Win8 laptop with Core i7” as the Server, provided it has enough RAM (8GB min 16GB preferred).
But be aware that you will need the Server to be a Domain Controller/Server combination, or else you’ll have to use one of your other computers as a separate Server.
To keep my costs down, I run everything on my laptop that has the minimum 8GB of RAM. But my laptop is running Windows 7 and I have virtualized my whole lab using VMWare Workstation. My Virtual Image runs Windows Server 2008, R2 (for PS2010) or Windows Server 2012 (for PS2013) and I have a combined Domain/Server configuration in the single Virtual Image.
I originally had the Domain Controller split out to a separate VM, which I then ran on an external drive. But I found that by using an SSD Drive, everything runs well (performance wise) within the single Domain Controller/Server based VM.
Let me know if you need additional detail on how to configure a useful, yet not too expensive lab.