Documentation: see https://doc.turris.cz/doc/en/start and this forum. I don’t think there’s any other larger source.
DNS
The default server on Omnia is knot-resolver.
For ad-blocking there are two common approaches – adblock package and DNS via pi-hole. I have no idea what “beefing up” means; knot-resolver is rather flexible, at least in principle.
Sci-Hub: I didn’t read details, but you can easily inject custom name-IP pairs, as described in wiki.