Rigth hand position.
The majority of bluesmen put his pincky finger facing his guitar. It permits most sure attack.
Left hand position.
A classical guitar player would be angry if he could see this book and the "folk" positions in fingerpicking way of playing. However, if you can see the Rev Gary Davis videos, Stefan Grossman perfomances and so on you can see "strange position" chord and the use of the thumb for building chords.
How many fingers?
You must choose. Doc Watson, Gary Davis, Mance Lipscomb, Merle Travis, Etta Baker... uses only TWO FINGERS (thumb and index). Mississipi John Hurt, Stefan Grossman, Dale Miller, Big Bill Broonzy and Happy Traum uses THREE FINGERS (thumb, index and middle). Marcel Dadi, Chet Atkins, Ton Van Bergeyk and Leo Wijkamp use FOUR FINGERS.
Can we use "fingerpicks"?
Rev Gary Davis played with plastic thumbpick and index fingerpick. Sfefan Grossman plays with a plastic thumbpick and two steel fingerpicks but only in the Rev Gary Davis tunes and Broonzy's songs. Marcel Dadi and Chet Atkins plays with plastic thumbpick and nails. The steel fingerpicks are not usual in the instrument's shops of the Basque Country. The most famous company is National but the Dunlop is one of my favourites in the 0.013 sizes
Arrangements
For ragtime-blues the C and G tones are fine. For blues, the most common are E and A. However you can see ragtimes in F or E. The legendary Merle Travis and also Gary Davis can play in B and F.
You can arrange all kind of melodies, but the 3/4 beats are not very common. For fingerpicking the 4/4 beats is the best way..
One of the secrets of fingerpicking arrangement is the feeling. Technique is necessery but not the first. Mr Grossman said: one arrangement is fine when it sounds like more notes than there are actually.