Not sure I understand the question about scaling, or at least I do not see the specific relevance to 3d printing ? The vertex clipping would hopefully be taken into account by your modeling software when you export to one of the commonly supported 3d file formats such as STL, OBJ, DAE or WRL/X3D. I expect if problems will arise it will be from subtle flaws that do not matter for a purely visual representation - coincident surfaces, tiny holes, sheets (like a character's cape) that have zero thickness. Familiarize yourself with the 3d output options (and perhaps even printability checks) available in your software (which is it ?), eventually download the free, cross-platform netfabb studio basic software from netfabb.com that lets you check for and fix some of the most common problems.
Printing in two or more materials is not currently possible, unless you can split your model into separate parts that you or your customers can assemble after printing. Multicolor printing is possible in a rather heavy, brittle material shapeways calls "full color sandstone" - actually gypsum powder held together by superglue and colored with a low resolution inkjet printhead. Trials are currently underway for a similar process using plastics particles instead of the gypsum, and an even more advanced printer type has been promised to become available later this year.
All the information about costs and required dimensions are contained under the "Materials" tab at the top of the page, you may want to view some of the production videos in shapeways' youtube channel to see how the actual printing is done and what level of manual work is still involved.