What you want to do is setup 802.11q vlan trunking between the switch and pfSense and again between your AP and switch.
Change switch for GS108T to support management, vlans, etc. Apple AirPort does not support VLAN or multiple BSSID (you only need one AP to run mutiple BSSID unique networks, unique security settings, unique LAN when used with VLAN) but I think all WRT54GL will be new enough to support multiple BSSID. Most likely your choices will be limited to DD-WRT (recommend Broadcom), Cisco/HP/Symbol/etc, ubiquity or other specialty vendors. The only reason I can think to keep Apple Airport is if you want to use the Time Machine backup feature, otherwise it's (IMO) just an overpriced sub-par consumer-grade router, not even a web UI or even CLI, no wall mounting, when all other routers have 5 ports, they have 3.
For the bandwidth limit you can do it easy with captive portal, just type in the speed limit.