King,
I am not sure torque or rigidity would be your primary concern, but rather chipload and surface footage. I work on CNC routers and CNC metalworking machinery, in general CNC metal working machines are substantially more rigid than CNC routers. The drawback for you is acheiving sufficient RPM to get a quality finish in wood with the limited rpm window present on most metal working machines. The reason you take lighter depths of cuts in metal, is because, well, its metal.
I think this comes down to how economically you want to start out producing these,(( which are super neat, (I want a set for my kids!)) If you are unsure of your forecast, demand, etc...want to increase these at a substantial rate but are unsure if the application warrants purchasing a mid to lower end router, I would say you could purchase a CNC assist style mill (bridgeport, chevalier, etc) with a basic two axis CNC assist style control for a relatively economical price. Then the problem becomes rpm, this can be stepped up with aftermarket style "speeder" heads. I feel comfortable that with the quill fully retracted, and the speeder unit and bit in place, rigidity will never be an issue. The drawback is you will probably never achieve an rpm sufficient produce a surface finish that eliminates sanding. Whatever type of machine you choose, you will need jigs and or fixtures, I do not see where you would need that many of a different type, but rather many of the same type.
Do we get free toy sets for responding to this post?
I hopes this helps and congratulations on a very neat product!
MarkT