Currently i use a Netgear GS748T managed switch for my VLAN's
Please have a look for a Cisco SG-300 or D-Link DGS-1510 that are Layer3 Switches and they
are routing the VLANs without the need of a router with neraly wire speed!
but my current router (Fritzbox 7490) does not support VLAN tagging.
Together with an Layer3 Switch you might be able to run your FB 7490 and let the Layer3
Switch do the entire VLAN routing and you don´t need really the pfSense.
I do have a spare Intel I3 2120 CPU free so this could be an option.
Any desktop CPU over 2,0GHz and higher might be a really nice candidate to get enough
speed for your action.
How much memory shoudl i be using if i also want to use VPN options and reverse proxy?
Do i need extra NIC's (besides 2)
2 GB for the base system without other packets should be right
4 GB together with Snort installed and VPN tasks
8 GB together with Squid, Snort and VPN tasks or Captive Portal might be a good amount of RAM.