Diffferent players are going to tell you different things. I'd say get a plectrum banjo with a resonator on which has lots of volume - you've got to be heard over a pretty meaty bunch of blowers and a loud drum kit and bass - you may not always have a PA, and IMHO bands sound better without them anyway. You can tune it like a plectrum banjo CGBD but you may find it better as a guitar player to tune it DGBE, so you'll know a lot of chords already. You need to play the chord inversions you get further up the neck than most guitar players are used to - the higher pitches up to say the 12th fret tend to penetrate and carry better, while below the fifth fret the chords will vanish under the weight of band.
Start with the key of Bflat, which many tunes use, and learn the 1, 4 and 5 chords and their sevenths for a typical 12 bar blues sequence. Listen to a lot of the old records, try and play along with them. Work out the chord sequences.
Takes a lot of time and concentration, but I don't think you can do it without, unless you can find a teacher.

Good luck with it.
Ray