I have so many questions!! Sorry if anyones head explodes!

I am a CNC Hobbyist and have started making a CNC machine, altho I have a couple of alternatives lined up if I fail. One thing that baffles me is the software. I have Adobe Illustrator as I do vinyl graphics and this has a dxf file export function. I want to do 3D cutting, some nice childrens cartoon characters for doors etc... Now what is the best way to do this? I am a student so can get Rhino3D cheap and have read some good reviews, unfortunately RhinoCAM is too much but I've read again that you can use cut3D. Can you import an already drawn picture and then create a 3D effect for cutting? As I have tonnes of pictures in vector format I use for the vinyl cutter.

How do you set up layers for the machine to cut correctly? I've played with lazycam and mach3, the simulation part but I cant see how you would do it. Is it an automated process when you have created your 3D image? and how do you tell the machine where your piece of work starts and how deep the wood you are using is?

The software bit is stopping me really from wanting to build the machine as I have no idea! I cant afford the massive software packages but have enough for the student version of Rhino and cut3d so any variation on software would be good aswell.

Many many thanks!!