Wow...a LOT of questions. Good ones though. A real good start would be to get a few CDs. Fortunately they're easy to find these days. Actually I'd be surprised if CAMSCO (Mudcatter Dick greenhaus' company) can't get everything you need in one gulp.

My suggestions:

Blind Willie McTell, Blind Boy Fuller, Brownie McGhee, Buddy Moss, Rev. Gary Davis.

Each of those players used an opposing Thumb/index (or thumb/index and middle) style and are highly rhythmic.

You might also check out the best of the white players who worked in that style.

Sam McGhee, Roy Harvey, Dick Justice, Leonard Copeland.

Hope that helps for part of it.

Rick