Hi soltech2,
Since you'll need to work in 3D, you'll want to take a look at packages like,
Inventor,
SolidWorks,
SolidEdge, for mid range modelers, or
Pro/E for a higher end modeling package. There are a few others
Alibre,
TurboCAD,
Rhino and
SketchUp. I haven't done much with the last 4 mentioned but they're worth looking into. I have worked with the first 4 and like them all, Pro/E may be a bit of over-kill for you want to do, but you should investigate them all - my personal preference is SolidWorks - great training, great support, great software package. SolidWorks was designed to go from "Art to Part" which is what I believe you're trying to do. SolidWorks, and Pro/E both have available add-ons (read as extra) software for creating G-Code for milling machines and the software for optimization.
All three will generate STL files for your prototype machines (3D printers). For milling machines, check out
Taig, or
MaxNC or even
Sherline. But even better for your milling machines check out these guys over at
CNCZone. They're very knowledgable and helpful.
If you need computers etc., make sure you decide on software first as they will all make recommend certain hardware requirements to best run their software.
Finally another option if you get overwhelmed with all of this, is to use someone elses machines like
EMachineShop.
Anyway, lots of options...
HTH
Todd