Hi
You have 3 options here,
1. You can bridge the hub 5 (disable any and all higher functions) and use the R7000 for all higher functions including PPP, DHCP, Firewall, Wi-Fi etc.
In order to do this you will need to access the Hub 5 (the default gateway should be 192.168.1.254). You can access this by connecting to the hub and typing the default gateway into your browsers address bar.
From there check that the firmware version is 4.7.5.1.83.8.200 or higher (this will be shown at the very bottom of the page)
From there you can enable bridge mode which should be under "Advanced Settings" > "Broadband" > "Routing" > Bridging= Yes"
You will then need to set up the R7000 (you will need to unplug the computer then plug in the R7000 and then reboot both)
2. You can treat the R7000 as a wifi repeater which does not require the BT hub Wi-Fi to be turned off. This Netgear help article shows how to do this, you may want to use this in conjunction with "Powerline Adapters/ Homeplugs" to get the best coverage.
3. Improve the Wi-Fi signal on the BT Business Hub, this can be done by looking at the available Wi-Fi channels and the signal strength of each, Apps such as "Wi-Fi Analyzer" and "inSSIDer" will let you see which channel has the best rating.
You can then go to the router menu as explained above and then go to Wireless and change the channel to the one with the best rating.
Hope this helps
Burkem5