Ok, I got everything set up and working. Had to restart some machines for everything to take effect, but it's running and working well.
Here are the settings I ended up using – seems obvious now that I solved the other issue, but this may help someone else get set up quickly, so here we go:
Under Basic > Network. The DNS 1 and DNS 2 won't appear until you change DNS Server to Manual.
The IP address of my pi-hole machine was 192.168.1.21 - you should substitute with the ip address of yours, naturally.
Under Advanced > DHCP DNS these are my settings.
On Pi Hole Settings > DNS this is what I have.
So far so good. I'm most pleased with the in-app ad blocking on my phone... 