About the stepper cooling i guess you can have different solutions.
For the Stepper at the bottom (Z axis) you might have some aluminum orcool ventilation shaft coming from the bottom.
For the other motors or hot end heatthink you might require to add external ventillation tubing taking fresh air from the outside f the box and creating airflow inside the tube up to the motor/hotend heatthink.
That's all i'm thinking about but i never tried to make one.
I saw a few times ago a guy printing a Kayak:http://www.grassrootsengineering.com/blog/mymachine/
you can see his machine.
He mainly managed to have all hist motors outside of the box.
And for cooling his print he has a ventilation tube with air coming from outside.