I like your drawng!!
But not sure why you need or want sg300 in l3 mode? I have 4 segments running 3 physical and 1 vlan, with esxi hosting pfsense and multiple other vms.
sg300 is just L2.
I can put together a drawing sim to yours.. But in a nutshell pfsense has leg in each vswitch which is tied to physical network for wan, lan, wlan and vmkern. vmkern is in the lan - but I break out a 2nd nic for it when it shares a nic peformance to and from the database is hindered.
dmz is jut vswitch with no physical connection and wlanguest is vlan that runs over the physical wlan segment. I also have another smart L2 switch netgear gs108t that there is trunk between it and the sg300 for the different vlans. I have my dvrs in the wlan segment and printer example for ease of airprint.
I think using L3 on your sg300 is just making for a more complex setup.