Try googling polarbot for some stepper driven ideas. A number of wall drawing gadgets use the same kind of mechanism as the Maslow and often use steppers.
For your stencil have you considered printing it on multiple pages, taping it together, and using an xacto knife? For longer life tape the pattern to stencil material like mylar or stencil board. Use a stencil spray glue on the back to help prevent paint from wicking under the stencil