I am using opnsense on mini-itx, for me it is ok because I have slow internet. Then I have unifi switch and two AP. My net is just 1g speed and it is enough for my family. Probably if I am going to upgrade I will stay in this setup, I mean router will be running opnsense and switch and AP will be unifi devices.

dont forget, cat6 can do 10g speed but if I remember correctly only up to limit distance.

maybe you need that speed, but mostly between few devices, e.g. server and workstation, so I think that you can use smaller switch for that.

maybe you already watch Toms video comparing pfsense and unifi firewall