In regards to the drive axles it'd be possible to design in Technic lego wouldn't it? The pulley knobs
can be glued onto the axles eg.
Run the spring as you say and then attach a pulley;
The motor can have to one way clutch pulleys on it therefore providing the drive.
The cartridge drive axles can intermesh with the lego axles and theres your drive, and to be honest they may be able to be made from lego parts as well.
Heres a motor that could be used depending on size requirements although rpm would be the limiting factor.
Since one of the ideas was to make it possible to fix nearly anywhere lego is pretty common all over the world. And if people are going to build this most of us would I figure have used lego in the past.
And some of use may still use it now