So I moved a few months ago, and only just now had time between work and school to set up my smart home again. Which turned out to be a sort-of blessing, since HA did some updates and the one for sensor and binary sensor templates dramatically screwed me as I template a lot. It also gave me the opportunity to upgrade my Yellow's Pi module, and I found (though haven’t installed) an internal z-wave module for it, which I'll do when I'm off for Christmas and New Year.
However, since I am starting fresh, I thought I'd ask around on best practices. So I use the Orbi Pro 6 which has three primary and one guest SSID, and I have it behind a Google router in its DMZ because we have Google Fiber here. Which also turned into an advantage because I wanted to a.) do full IoT isolation and also b.) have someplace to put my singleboard computers and my servers that's safer but still have internet access plus c.) avoid wifi congestion (three VLANs plus the primary router's wifi takes care of that nicely).
On the Orbi: VLAN1 is primary and where I keep my singleboard computers, my servers, two TVs, X-Box, Switches, and my laptop. VLAN2 is for IoT hubs, cameras, Roomba, etc. VLAN3 is strictly lightbulbs, which sounds ridic but when I did a wifi analysis they really really super really take up a lot of wifi bandwidth, I've been slowly replacing with Hue and other zigbee, but it's in progress. I may move the cameras there as well.
What I need to figure out is the best way to connect everything to Home Assistant. What I was doing was attaching Yellow to VLAN1 by ethernet and VLAN2, VLAN3, and the primary SSID by wifi. On the Orbi router is an mDNS gateway page so I set it to connect my VLANs so they can exchange some data.
But now I have some time to design, and also, I can run multiple instances of HA on one of my servers. I had been doing that anyway to test any chances and test and run Add-ons that I wrote myself, just not a permanent one (again, test instance; I murdered it a lot and spun up a new one when things got weird).
So for anyone who deals with multiple SSIDs or VLANs (or just has an opinion): keep Yellow as is or go with the multiple instances and use Remote Home Assistant (which I used with my test instance and it worked very well) to send entities in the VLANs back to Yellow? Anyone?
It might be a tangent: In my understanding this does not work as you might think. Unless your Orbi actually uses different radios for the different WiFis they will still have to share all available resources - no matter the SSID. Are there really Orbi devices that use different radios for different SSIDs (apart from the obvious 2,4 GHz and 5 GHz + 5 GHz mesh connection).