But as far as setting the subnet for the interface, do I do that through pfsense?
On PFSense go to the menu 'Interfaces' then to 'Opt1'
Set 'Bridge with' to none and
Set the 'IP configuration' to something like 10.2.0.1 / 24 or you could use 192.168.2.1 / 24 your choice on the IP you want.
Services -> DHCP Server -> Opt1
And set up a DHCP range for your optional interface.
Firewall -> Rules -> Opt1 tab
Action: Pass
Interface: Opt1
Protocol: any
Source: any
Destination: any
Description: Opt to Any
That should be enough to get your Opt1 interface working for a laptop or anything connected to it.