I’ll make a note here that a firewall is useful for internal traffic, too. Those IoT devices can get pretty annoying, so you’d want to e.g. drop your cheap webcams into a VLAN and disallow them from talking to enjoying but their cloud, and especially the other VLANs, or isolate Alexa capable device so it won’t try to figure what else you got there in your house over mDNS (it will).
A managed switch would do nicely. Having isolated ports on the switch (and the wifi AP) is also great if you want to make sure the specific device will only talk to the gateway and not its peers.