Wow!! you sound like a man with a plan.

I have nothing positive to contribute, and can only recommend you start sketching up some plans, which will start the feedback coming..

I made a servo, (of sorts) once, using an arduino... this wasnt for cnc use though (it was used for power steering on my lads toylander)

intrigued as to how you intend to tackle some of the design challenges you have suggested (ie, milling steel and titanium), no doubt you have a plan

look forward to your responses... keep the ideas coming. Sometimes new threads dont attract many replies until you start posting pictures :D