moshing,

what you are asking for sounds more like a bespoke application.

Its going to need to have a proper interface for talking to the bluetooth phones.
I dont think you will find a "--museum-mode+bluetoothsend" specially designed into most software.

As for sketching, liqbase does a good job at covering the OS and being a fullscreen application in active development could be tailored to your needs.

Images can be saved as png at present, not sure about a bluetooth interface, but you will tell me how important that is, have you considered simply uploading sketches at the end of a day or as required to a webserver?

might be more flexible and would allow the smaller phone free visitors to use the device.

The last I heard about you was you were doing software updates of things and wanting to do things automatically via a cron job, did you manage that?