Recommended add in network cards would be Intel i226 for a single port and Intel X550T2 for two ports. Both do 2.5Gbps per the Intel documents. Realtek is not recommended and is usually on consumer motherboards. Works fine for some users. Others have problems with network drops, etc.
I don’t know if OpenWRT works on TrueNAS as there was a recent forum post asking. How to install OpenWrt in TrueNas Scale VM (23.10.2)
You might have trouble with PCI-e slots as Graphics Card, HBA and NIC are all desires. You need to verify what kind of slots those all require.
Proxmox, please read the forums here as it has to be set up correctly or it causes trouble with ZFS and TrueNAS. Usual advice is pass through the entire HBA for the data disks. Boot disk needs protection from Proxmox also, there are a few ways?