Well, of course, it has to be all-Bach.  Because everyone has different
tastes within Bach's ouvre, no Bach concert is likely to please everyone,
but that's no reason not to try!  I don't know a thing about programming
for a concert, but here's an all-instrumental list with some variety:

   Orchestral Suite (Ouverture) No. 1 in C major

This should provide a nice introduction.  Actually, all I heard in my mind
was the opening notes of the overture, but all the movements are very
lovely, gracious, rhythmic, and the sound can be really gorgeous, HIP or
not.  In fact, any of the orchestral suites would work, and would probably
be new to practically half the audience.

   Trio sonata in E-flat.  Transcription for instrumental trio.

This organ sonata is one of the most perfect minatures I know.  It has been
performed successfully as a flute/violin/cello trio, and I believe it would
work well if transposed to C major and the top line played on a recorder.

   Brandenburg Concerto No. 6

This is (of course) basically a septet for two violas, two violas da Gamba,
two baroque cellos, and a keyboard continuo instrument.  I would love to
hear this work with the soloists arranged in a shallow arc in front of the
audience, so that the antiphonal portions sound nicely separated.  If a
rousing finale is appropriate or necessary,

   The closing movement from Orchestral Suite no. 4

would be all the pomp and glory one could want.

Arch