Look for Intel I350-T4 on ebay. Buy a used one that looks like this . Some of the cards have these little metal tabs on them . If you can, avoid buying one with them. If you get a card with them, not an issue just takes some more care putting the case panel back on. Do not buy one that looks like this (note the larger metal bracket on the bottom of the card, the baffle might not fit it) You are also going to need the baffle (aka the bracket). I bought the riser and baffle together from this ebay seller. I run OPNsense on a m920q as well. Since you are learning, I'd recommend installing Proxmox on the m920q and running OPNsense as a VM. This is how I have things setup Even though I have plenty of IT experience, being able to snapshot and backup VMs before making potentially breaking changes is always preferred.

did you settle on a nic? what'd you get, what worked?

Nice work and thanks for the tip! I was able to get WS2022 running properly on my M720Q using these steps.

https://forums.servethehome.com/index.php?threads/lenovo-thinkcentre-m920q-with-intel-x550-t2-fru-00mm860-made-practical-with-3d-printed-bracket.32069/ It's doable, apparently

I recommend Intel X550-T2. It is verified to be compatible with ESXI.

On the network card I would aim for either the i226 or any Realtek 2.5GbE network card. I don't believe there's any particular advantage to having a known brand for the card, and Intel made such a big mess of the i225 series that I would stay clear of it. The i226 is, as far as I can tell, "just" the fourth (!) revision of the i225 and rebranded because the series has such a bad reputation. Alternatively the Realtek chips are generally all good at 2.5G. For the switch, there are very few, if any, second hand enterprise switches that support 2.5GbE on the market as far as I can see. The Brocade switch consumes a fair amount of power just being turned on, it's enterprise equipment and that's their nature. I don't think there's much point in going 1GbE ports in 2024 either if you intend to keep the switch for a while. The prosumer gear only really makes sense if you are going to have multiple components from that vendor - switches, firewall/gateways, APs etc. Switches larger than 8 ports quickly get expensive and PoE adds cost too. If I was you I would get started with one of the cheap 8 port 2.5G + 2 SFP+/10GbE managed switches, Serve The Home has a big roundup article on them. You can also look at Mikrotik. That way for $200 or less you can get started with a small switch that will cover your needs for the next couple of years at least. If you have some non-lab gear - TV, Xbox etc - you can always aggregate them with a cheap 1G managed switch. I bought a couple of the Hasivo 5x2.5 2xSFP+ managed switches for edge aggregation and they've been fine. They also provide the PoE for my APs so my main switches don't need to do that, making those quieter and cheaper to buy. The management UI is very basic but it does everything you need, plus after you set it up you really never have to mess with it again.

FWIW, I ordered the same card from AliExpress for my HP T630 thin client (didn’t want to use the SFP option that’s typically recommended), and it works just fine. This board is really a hidden gem for any USFF build where a second gigabit port is needed. edit: HP T630 thin client - not a Dell tower