Pfsense as firewall on VM for windows server 2012

[Armando Alvel]

I have WS 2012 R2 giving Internet to a simple LAN. The Server has active two NICS, routes the packets and served the Lan with DHCP. It has also Nxfilter as a DNS/filter server and Squid as proxy. (I found all this done by people before me)
The firewall of the server has been configured with the rules of the basic farewall of the Lan's interface (inb/outb on NIC properties) and I'd like to change that. I would like to sostitute it with PfSense running on a VM (Virtualbox or Hyper-V) inside the WS 2012 R2.
From PfSense I need just the firewall (so traffic Lan - Internet passing through it), don't need routing or dhcp for the Lan. I prefer leave this as it is now (Server doing it)
My questions are:
a) is it possible?
b) how to configure the virtual NICS for the VM of Pfsense. Bridge to Wan and bridge to Lan? I have squid on port 3128 of the Lan. Does it affects?
c) Is it necessary to configure both interfaces in Pfsense? And if so: may I leave the WS DHCP serving the Lan?