the problem is simple, I often work with models that are prepared for animation. So lots of planes, non closed object and so on. For 3D print I need to close all holes, make planes solid and merge all the object so there are no intersection. This is a hell of a proces when the model has about 200 pieces and you have to check them all and the process has lots of errors, is there something that makes this kind of automatic?
Have you tried the blender 3d printing add on?. If that hasn't worked, I'd suggest exporting a selection and attempting a different workflow. That article's goal is to create a mold, but the software it uses (Meshlab, Meshmixer) can help you accomplish some tasks. Some very complex models I have found hard to do everything automatically. Further, if you are working with slicing, I would recommend chitubox. It automatically hollows models and creates supports.