Regarding your Zigbee and Zwave devices, all of your Zigbee & Zwave devices should be connecting to a hub which then connects to your network. Whichever wireless router you use should not be an issue. Regarding Eero, you are correct. Guest network devices are segregated not only from the main network, but also from each other; the only thing they can access is the internet. They can’t even see the Eero itself, technically.
I would stick with what you are familiar with Asus, take a look here for the new Wi-Fi 6 Tri band Mesh solution. If you do go with this then I would ditch your existing router or just configure it to handle all of your IOT devices since most of them are only capable of 2.4 Ghz.