You cannot pass the nic through and still use it in proxmox - it loses all access to the nic. So if you want to go that route I recommend you to use eth3 as dedicated port for proxmox.
For (2) - affected in which way? Compared to which baseline? Are you concerned that your machine cannot keep up with 320Mbps? I doubt that.
For (3) - depends on your local network setup. Do you use vlans that need routing? Then it goes via OPNsense. Otherwise if all devices are in the same subnet, it likely will not.
For (5) - no loops. You're not routing traffic between eth3 and eth2.
You cannot pass the nic through and still use it in proxmox - it loses all access to the nic. So if you want to go that route I recommend you to use eth3 as dedicated port for proxmox.
For (2) - affected in which way? Compared to which baseline? Are you concerned that your machine cannot keep up with 320Mbps? I doubt that.
For (3) - depends on your local network setup. Do you use vlans that need routing? Then it goes via OPNsense. Otherwise if all devices are in the same subnet, it likely will not.
For (5) - no loops. You're not routing traffic between eth3 and eth2.