I've written the step I used to do the DoH part.

https://www.aaflalo.me/2018/10/tutorial-setup-dns-over-https...

Still need to document the PiHole part.

I've also disable all logging for Nginx and Pihole. The server is also listed on https://dnscrypt.info/public-servers

Also, if you're in the American Continent, you might want to use the proxy I setup on Google Cloud Platform:

https://dns-gcp.aaflalo.me/dns-query