The major question that first needs to be answered is, do you have to
end up with a cosmetically interesting unit that is both an organ and
a string unit?

A search on Google will show a number of large keyboard operated
claviorgans.  To build something like these would be a very major
engineering undertaking.

By far the simplest thing to do would be to have a separate organ and
a separate harpsichord type instrument.  You can send a MIDI signal to
both simultaneously.  MIDI-operated pipe organs are easily available.
A number of people including myself have converted harpsichords to
MIDI operation.

Phil Dayson