The thicker the pick, the more bass you'll get. If you want a more trebly sound, use a medium. A thinner picker tends to brighten to higher harmonic...
As far back as the mid 70's I was messing with some guitar-derived fingerpicking on the mandolin. There were some Happy Traum books on Oak that I had...
Just the flesh of the fingertip. Pick + finger(s) really allows you to do stuff you couldn't otherwise do. For samba chording, the "pinch" gives you...