All coordinators in all solutions have a limited direct connexion (not the same for all solutions).
In a zigbee network you have 1 coordinator (the gateway), routers (for exemple bulb, plug, curtain, generaly all powered devices), and end-device like sensors.
The coodinator always have limited direct connexions, but it's not a problem because you can use a router to increase this number, the router use 1 connexion to the gateway and purpose itself more connexions for other device (and it have too a limited direct connexion number).
So yep, you can use a second stick as router but you can too use a simple bulb. The problem is all hardwares aren't as good as router as other, philips bulb are good router for exemple, and on the 3 solutions you have cited, all do not handle routers as well on a zigbee network with differents manufacturers.
On my side I have finally choose deCONZ. So yes, you need to install deconz and no more thing to install, no libs, no mqtt server, no more applications. You have a webserver in deCONZ, so you just need a web explorer to connect to Phoscon
https://www.dresden-elektronik.de/funkt ... n-app/?L=1
You can do all you want in this webapp, with a more "sexy" UI than the domoticz one (take a look on the previous link), pairing/scene/manage device/make groups/ect ...
After that, just run/restart the domoticz plugin, it will sychronise domoticz with deconz, and create itself devices to use in domoticz.
And it s finished. Even for update the firmware you can do that in the webapp. I don't think you can find more plug'n play than this solution.
The only configuration you have are plugin setting, and use blacklist for device you don't want to see in domoticz.
You can set scenario/scene in deconz and you will have a push to on button in domoticz to trigger it, or you can set them in domoticz if you want to use a scene with zigbee device + wifi devices for exemples.
And for "power configuration" you have the deconz utility
https://www.dresden-elektronik.de/funkt ... econz/?L=1 this one need more attention but you don't need it for normal use. You will need it for custom configuration or devices not natively supported by deconz, but not so hard to use, it works with drag'n drop et select cases.