Well depends on your current setup. If your current setup is a 1 WAN and 1 LAN(No Vlans) and your ISP doesn't use PPPoE or similar it should be out of the box good to go, exept you needing to maintain it aka update and monitor. You can setup auto updates but checking logs and maybe setting up IDS/IPS would be a good idea.
What do you mean "ditch a router" pf/opnsense are firewall/routers. If you want WiFi you will need a AP(Access Point) that can either be a dedicated AP like what Ubiquity offers or a WiFi router that allows you to disable all "router" features. As for dongles I would think that it's a bad idea. I personally use a Unifi 6 Lite that is running OpenWRT. Also I use Opnsense due to the hardware support and it having a better layout in my opinion also some nice to have plugins.
Also if I was you I would recommend OpenWRT it might be a better fit :)