You cannot ad blocklist in batch in AdGuard. Also developers are from Russia with headquarter in Cyprus.
I’m currently happily using https://nextdns.io/ but I don’t thing you can install that on a Raspberry Pi.
I also think for DNS blocking you're best off just adding one list and being done with it. Adding lots and lots of lists only opens you up to more fault positives and problems down the line IMHO.
Most companies have an "about us" section with info where at least you can see who the people/management are.
Instead, they provide a vague page: https://adguard.com/en/contacts.html