"oops. have just bought this very hardware for an alarm upgrade"
I recommend you discover the joys of multiple VLANs and multiple SSIDs. 1 for your PCs/laptops, 1 for NASs/servers, 1 or more for IoT stuff, 1 for your phones, 1 for guests. Each will need routing, and a good firewall policy. It's non trivial but necessary if you want a modicum of security.
The trouble is, not only is it a bugger to setup the above properly but you will need a bit more than your average ISP freebie router to do it. However get yourself something like a Draytek or FritzBox or a custom ROM based thing like Tomatoe or pfSense on an old PC/laptop plus a modem as required and you can do all of that. Reasonably cheap switches can be had eg Netgear GS110TP for PoE + layer 2 managed for cameras and the like.