I certainly want re-entrant tuning. I read where that banjos mostly use DGBE tuning which, of course, is lower than GCEA tuning, but it doesn't sound as low as my baritone Uke. So I'm a bit confused. Do tenor banjos (4 strings?) clawhammer?
OK
multiple issues here!
Four-string (tenor) banjos are tuned (usually) in one of four or five tunings, which may or may not depend on whether it's a "short scale" or "long scale" instrument and for which style of music it's being used for. None of these tunings are usually re-entrant.
There's GDAE, 5th's, which has the widest range and is the same as a mandolin or fiddle, but an octave lower, usually on a long-scale instrument. Then there's CGDA, again 5th's but about half an octave higher, like a viola, often on a short-scale instrument. There's the "normal" banjo tunings, CGBD or DGBD, much like the 5-string banjo, but without the 5th "drone" string, or there's DGBE, the same as the top four strings on a guitar (or baritone uke), which, for whatever reason, is often termed "Chicago" tuning ... confused yet ?!?
To my knowledge, none of these tunings would normally be used for traditional clawhammer, which is usually recognised by the treble drone of the fifth string under the thumb
*but see below for update*
On a re-entrantly tuned four-string instrument, as per a "normal" ukulele, one can perform a passable representation of many clawhammer tunes. They won't be "the same" as they would be on a five-string banjo, simply by virtue of not having the overall range, but they can be very recognisable
For your purposes, you'll either have to take specialist advice on string gauges, or do a bit of experimentation. I don't have reservation about using heavier gauge nylon strings on a banjolele, there shouldn't be a stress issue, especially with a re-entrant tuning, but never having tried tuning a concert-length instrument down several semitones, I'm in no position to make any recommendations for string gauges.
I wish you success with your project. I'm sure it's possible and I hope you're happy with the result