What is the correct ownership for subdirectories in /usr/local
Out of the box - root:wheel has ownership of /usr/local and 0755 permissions. It's really up to you what you want. Since you clearly have homebrew or remnants of that, I'd do whatever brew doctor says you need to do for the user account you want to run things. I'd say keeping user:admin permissions is just fine for almost all cases in that part of the directory.

I have user:admin and 0775 permissions on everything but /usr/local itself and /usr/local/remotedesktop which match and are root:wheel with 0755.