I tried using it on several occasions, but it is extremely slow for me, with occasional visual glitches… I use Wayland, if it makes any difference. How’s the OnlyOffice performance for you? Maybe I’m doing something wrong?

Like other people suggested here, use opnsense instead of pfsense, and wireguard instead of openvpn. What I did for my homelab was to get a used HP t620 thinclient and an Intel 350 card with 2x 1gbps ports. You say you have 10gbps, so you would need a card that can handle that, and maybe a beefier CPU. For my setup, this tiny 65€ machine is not even feeling it. Single digit cpu usage for 2 wireguard connections, a little over 1GB RAM usage for a handful of services. I think for you an n100 with 4gb of ram is more than enough, but going for 8gb will be better and it will not be much more expensive.