I quickly checked the manual and youtube.
I can’t immediately see a way of killing off the router half. The manual makes it look like you have to setup QuRouter before it even give you QTS.
If you setup QuRouter, go back to it and change the mode to Access Point.
And then see if you can disable the WiFi. (or if it has better WiFi use it 
)
The default router mode makes it seem like QTS interface options don’t stick.
Manual also doesn’t tell me anything about what the Host port really is.
I want to say Host is for the NAS, and the router has Wan, lan1-3.
Set everything DHCP in QTS and try to put QuRouter into AP mode.
It should not matter what RJ45 port you use after that.