It's a little bit more complicated than I made out. For one, the network is super unstable and restarting the ISP router seems to fix it. I want to replace the router to test the theory that it's the problem.
Secondly, this is a bring your own router to the ISP situation, but the router came from another ISP, but they are all the same ISP in the end because one company owns a whole bunch of ISPs and sends the same router to all the customers of all the child companies. Long story short, it's the router they would have issued to me, but they didn't, because a different subsidiary sent it to me before I changed ISPs to take advantage of a special because I live in a country where the lines are open and anyone can start an ISP using the existing lines but if you get big enough to be competition then the big company will buy you out and pretend it's still a separate company. But if it doesn't work well then it's up to me to solve unless I am willing to pay the ~$10USD for them to send me the ISP router that is supported by them but it will be the same cheap router as I already have. Ok that's not a very short story but that's why it was easier to just call it an ISP router 😆
One of the things I use pi-hole for is to set customer DNS entries so anyone on the network will be redirected directly to the self hosted services when the type in the appropriate domain name. So it's not just about the filtering (which I also want), but also the (network wide) custom DNS entries.
I'm also happy with simple. I'm not overly against keeping the pi-hole and gateway separate but was just wanting to know if combining them would be an option (which is sounds like it is, but not super easy).