I worked with Circuits, LLC last year when doing my first flex boards. They have a downloadable design guide linked on their site that will probably be helpful. You'll still want to talk to them after reading the design guide, since there are different design optimizations for a "static" flex (flexed on installation but doesn't move much afterwards except for equipment vibration) and a dynamic flex that is in motion throughout the equipment's service life. For example, a static application can live with a via or two in the bend but you really want to avoid them in a dynamic application.
As far as documentation, I just needed the standard Gerbers + drill file and a separate CAD file with the outline of the complete board and the locations/dimensions/fittings for the rigid frame elements and material specifications.
#include < std_disclaimer > // Just a customer