Preparing a Model for Printing

Hello, I’m a beginner in the world of 3D Printing. I have experience as 3D modeler, and I’ve been specialized on horses sculptures. Now I want to print my models on Shapeways site because they cast the model in bronze. The question I have is if someones knows the technique on how to hollow a model of a horse. I has been watching some tutorials on YouTube, but only covers heads but not four-legged animals. Also on how many polygons the model will be to keep the balance on detail and small file size.

I use Blender for modeling.

I apologise if this question is too silly or does not fits on this forum.

Thanks in advance.