1) It depends on the stop list on the organ. If I were using the organ that I play, I would use the 8' Stopped Diapason and 4' Wald Flute on the great (though these are not solo stops). Solo stops are generally soft, and the flues described as liquid and you will get a nice sound. If I were using the Swell, which is probably your best decision, I would go for 8' Gedakt, 8' Gamba and 8' Voix Celeste; and for a more 'twinkly' sound: 8' Gedakt, 4' Stopped Flute and 1 1/3' Larigot, but dont use the bass too much as the sound can separate.
2) It can be: It just depends on the solo piece, and your preferences.
It is possible to couple the Swell manual and Pedals togeather with the 'Swell to Pedal' Coupler. In the baroque period, the pedal registration would mimik the Manual regestration but an octave lower (for the swell registrations I gave: 16' Sub Bass [or Soubasse] and 8' Flute; and for the second: 16' Bourdon and 8' Flute). However you can go for something really contrasting and use it only where it suits, even a reed. And dont forget, the pedal division is unexpressive; it stays loud.
Let get my Audsley too look up some nice ranks:
Dulciana could be nice, and maybe Clarabella (if the organ isnt very well maintained, dont use it).
Gemshorn, but that is generally on the choir.
Do you have a stop list for an organ near you? That would really help me in assisting your stop selection so I know what to work with. If not, do you know what style of organ it is because that affects the stop selection severly, and if possible what temperment (style of tuning)?
Hope I have been some more use,
Tim