The DNS function and the DHCP function are completely independent. The DHCP server function is useful in a few situations: (1) a router won't allow DNS assignment to Pi-hole, or (2) all DNS queries appear to come from the router instead of from individual clients.
If you don't have either of these problems, there is no compelling reason to use Pi-hole for DHCP.
If you do want or need to use Pi-hole for DHCP, then after you make the change in the router and Pi-hole, reboot the router and renew the DHCP lease on all connected clients so they get the new information.
I understand the difference between DHCP and DNS, which is why it's perplexing that routing stops working.
After I setup the pi-hole as the DHCP server and save, I reboot the main router (10.0.0.1).
Things go haywire at that point.
When I try to log on to the main router I actually end up at the login screen for one of the Netgear WiFi Extenders.
I can't even fix the problem until I turn off the extender.
I'm going to experiment again later. I've assigned the Extender a static IP of 10.0.0.150. I'm hoping it will not interfere (if it's the cause) since it won't be looking for a DHCP server.
The reason I want to use pi-hole as the DHCP server is that I'm weary of Netgear's crappy software for DHCP. It doesn't give me accurate information as to what's on the network and what IP's are assigned.
You should be. We will all stop buying Netgear equipment in the near future because they want your personal data so you can use their products in the future:
Starting from firmware version 1.0.5.4, product registration is required to unlock full access to the local browser UI.
You can login and access all features through the local browser UI 3 times without registering the switch through your netgear.com account.
A limited feature set is available without registration [...]
You can only access the router three times before you have to register? I have no word for this. When they do it for one of their average (not even high-end or professional) products, they will very likely do it for the rest as well. Either don't buy their equipment or directly replace their firmware by OpenWRT, etc.