I set up an RPi3 B+ as a router and access point using this guide. Currently things are working well. My Pi is connected directly to my cablemodem and traffic is routing fine.
I'd now like to set up Pi-hole on this same Pi, but its automated installer seems to want to build a bunch of configs from scratch. Currently I have dnsmasq running on 192.168.0.1 handing out IPs in my desired configured range, and also acting as my DNS server. AFAIK I basically need Pi-hole to respect that configuration but add its domain-blocking capabilities. But when the installer launches, it gives me a choice of interfaces, tries to use my ISP's DHCP-provided IP as its static IP, etc. It also wants to set a static gateway, which is already handled by dhcpcd via my ISP.
Is there any way to use Pi-hole in this setup? My router Pi is pretty under-utilized, so I'd rather not put this on another if I can avoid it. It looks like your DNS server is dnsmasq-compatible, so it seems like it should just be a matter of installing your own binaries plus configuration for DNS-blocking, but I haven't found any advanced installation docs yet.