Best thing to do is let your netgear do it all (router, dhcp and wifi). You setup the zyxel to switch off wifi and put it in bridge mode (if possible, ask your provider). Or otherwise forward all traffic to the netgear via a DMZ. That way you are also not dependent on the hardware your provider gives you and that makes it easy to switch to any other provider (cable, fiber, adsl, doesn’t matter)
Concerning the test not running anymore: try the new testversion of the app (see link above). Athom made some firmware changes to Homey making the test timeout too soon. In the new version I made the test run a lot shorter.