Can't get model manifold for 3d printing I got the following model:
http://doekewartena.nl/temp/sw_test01.obj

Which is kind of crazy. When I upload it to shapeways it tells me it is not manifold and it is unable to repair it.

I did remove all doubles. I fixed the holes I could find. I did the check with the 3d printing add on and there it is manifold.
So now I have no clue of what to do next.

Is the model just to complex itself?
Non-manifold doesn't necessarily mean double vertices (although there are quite a lot in your mesh). It could also mean that you have vertices inside your mesh. Import it into blender, tab into Edit Mode, then go to "3D Viewport - Menu - Select - All By Trait - Non Manifold". Try to delete the vertices and then try to verify on shapeways again. 

Your second question: I don't have much experience with printing, but I think your model is way too complex and it also contains ngons.