@anotherguy82 Tons of people run pfsense virtualized on Proxmox and I think the most common setup is to have dedicated NIC's for both WAN and LAN. And the preferred setup is to do passthru (IOMMU) of those NICs so that pfsense is the only machine accessing them (giving optimal performance).
So you assign two out of your four NIC's to pfsense and the others will be available to Proxmox and your VM's. Nothing other than pfsense WAN is exposed to the internet.
You have to make sure virtualization is enabled in the Optiplex BIOS to make this work though.
On the topic of VLAN's, yes your TP-Link Layer 2 switch will support that perfectly fine.