Hi John, so the main way for going to Cinema4D is to use the File menu (located in the bottom left corner), and use File > Open to load your CAD file and then use File > Save As to write out to .obj format to open in Cinema4D. A "Meshing options" dialog will appear and Cinema4D has good support for n-gons so you can use the option for "Output: N-gons" on that dialog to make a cleaner looking wireframe rather than all triangles.

Using File > "Save As" will save all objects to the selected file. You can also use File > "Export" as well which is short for "Export selected", it will write only the current selected objects to the selected file rather than everything like "Save As".

The main area of difficulty is if your files are pretty large. MoI v3 is still a 32-bit program and so can run out of memory when processing large files. This will be solved in MoI v4 which will be 64-bit. It won't be much longer before the first v4 beta release will be out. If you run into problems running out of memory there are some tips here which may help: http://moi3d.com/forum/index.php?webtag=MOI&msg=5322.2

Hope this helps!

- Michael