I fallen in love the camera and thanks to Johns explanations about the chemical tank . Its a marvellous idea. Can you post the postcards scans. I really want to see the lens emulsion performance. You can may be sell it to SF MOMA or Eastman House. Just post a thread to emulsion making forum here in APUG and PE can offer some formulas for your new papers and chemicals also.
I dont know Where you can learn its price but there are antique camera price guides . Please keep the prints safe sealed container far from the direct light and moisture. As someone said ideal is % 50 and you can protect them with humidifier tablets.