I'm trying to build a media server that will also work as a gateway/proxy server to control the bandwidth usage within home network.(Limit/Control the daily download and upload/Speed of each devices within the home network).

And at the moment, 
There're 3 PCs connected using Ethernet.
And another 5 Devices(incl. laptop) connected using Wireless

I have :
Dlink ADSL Modem -> Wifi Router -> 8port Switch -> PCs (Ethernet).

In a picture, it's like this.

I'm hoping to build a server with a motherboard with embeded cpu.

I'm wondering if I would require a Dual Port Server Adaptor (Link in Pricespy) to do the job.

Or can I run a server without needing Dualport server adaptor? (With only 1 gigabit ethernet on Motherboard)

ANY gateway/homeserver related advices would be greatly appreciated :)

Thanks guys