For wireless APs, Ubiquiti equipment is fairly well-priced and capable for prosumer gear, although I’m beginning to be less enthralled with the controller model for APs. They also can operate on 48vdc passive power, or 802.3af/at PoE, which might work nicely if you have a compatible switch.
I’ve heard from colleagues running Plex on Proxmox that core count is nice, except when doing transcoding, where you either want high single-corr performance or a GPU to offload. So an AMD Epic CPU might serve you well, if you can find one of the cheap ones being sold off from all the Chinese data centers on eBay.
Now with that said, have you considered deploying against existing equipment, and then identify deficiencies that new hardware would fix? That would certainly be the fastest way to get set up, and it lets you experiment for cheap, while waiting for any deals that might pop up.
Yeh, Id second running it on whatever you have kicking around, and figure out where to go from there.
Refurbished SFF PCs from ebay are quite popular if you dont have anything to hand. Easy to pick up a 4 or 8 core CPU, load it with ram and pop in an SSD. Onboard NIC will be fine until it isnt. Integrated graphics for transcoding is fine until it isnt. When they start becoming a problem, figure out your next step.
Can always repurpose the old hardware as either an additional node or as a proxmox backup server.
Edit: only thing i will say: if you are virtualising opnsense (or whatever as a router), its worth getting an intel pcie 4-port network card. It will let you “bifurcate” the 4 ports, so you can do pcie-passthrough to opnsense for WAN and for LAN (home network), and virtio the nic for proxmox bridge
The multi port NIC can work, although I would recommend jumping straight to a managed or enterprise switch that can do VLANs. It saves on physical wiring and a managed switch often overlaps with other desired homelab features anyway, like PoE, IGMP/MLD snooping, and STP or loop-protect.
Its more about having physical separation between wan and any of your networking. Removes a potential avenue of misconfiguration, and means you dont have to debug switch config, proxmox bridges/firewalls etc if your internet goes out.
Having a physical port for lan means it can adopt the default anti-lockout rules of opnsense (pfsense has similar). So mistakes on the firewall doesnt mean bricking your network.
And passing them through via pcie passthrough means you can never accidentally join a VM to the wrong bridge.
I had Ubiquiti for a long time, even deployed 50 at my work network. Switched to TP-Link Omada, much cheaper Ap’s, super cheap hardware controller (software option), and much more stable, longer-lifetime software/firmware. (updates are like 2x/yr - ish). The interface is so similar to UniFi that it is hard to tell who ripped the other off.