I set up pihole on my 3 and it was really easy! I don’t remember what guide I used, but they’re out there. I think I went with the official one on their site. The one tricky part was dealing with my ISP-provided router that kept me from setting a custom DNS.
Since the DNS options I needed weren’t available via my router’s admin page, I instead used pihole’s backup option for this scenario and used pihole’s built-in DHCP server: https://discourse.pi-hole.net/t/how-do-i-use-pi-holes-built-in-dhcp-server-and-why-would-i-want-to/3026