Thank you for taking the time to answer throughly! I noted your advice and chunked up my goals into "mini-projects", once I have all the configurations set and all devices connected to the new router. I did check what I bought is a router, not a switch (I find the naming of the device acting as the gateway between the LAN and WAN to be a bit ambigous: switch, router, gateway...).
As for the IDS capability, this is something that would be done by a raspberry pi being fed packets from the router. I don't know if I will ever undertake that task, but I keep it in mind if I'll feel adventorous 🙃
(for those wondering: Linux Magazine #279 has a guide on how to accomplish this with a Fritz!Box 7583).