I don't see the need for the second switch on the second pfsense, unless you plan on adding vlans.
In fact, you could, technically, run your public wifi subnet through the first pfsense box via the first vlan switch. Each vlan acts like a physical network with its own gateway on pfsense. You may, however, have other reasons for wanting to separate the wifi network totally, such as physical separation from the first network, or load limits on pfsense 1.