Pre-Beginner Questions

Kirk wrote:

Does LinuxCNC do the whole job CAD and CAM

No, LinuxCNC doesn't do CAD or CAM. LinuxCNC requires G-code as input, which is typically the output of a CAM package. There are some exceptions to tis, for example there are input filters that can accept certain graphical file formats, and there are add-ins for LinuxCNC that allow definition of simple (and some not-so-simple) features.

including driving the stepper motors and their position sensors?... Or are amplifier chips like IRF3708 needed to run stock motors?

LinuxCNC can generate the pulses to drive a stepper motor, and it has the ability to generate patterns other than step-dir, so it is capable of driving motors directly. However given that the average IO port can drive with about 15mA and the typical stepper motor needs 3A you pretty much always will need some sort of amplifier. The amplifiers also have the advantage of using current control, so you can run your 3A motor at 50V which gives a big increase in torque at higher speeds. (The current will still be 3A, even though the motor back-EMF might be 40V)

Can it run on a Raspberry Pi 3B which has 4 cores?

Good question. It's certainly not a commonly-used option with LinuxCNC. It might be more common with the MachineKit project version of LinuxCNC. Until quite recently there was no usable realtime system that worked for the Pi with LinuxCNC. You would need to install the PREEMPT-RT kernel on your Pi then check the realtime latency to be able to tell if the system was suitable. There are packaged kernels for the Pi2 but I am not sure about the 3.

Some posts I've read talk of using commercial daughter boards that aren't cheap and some boards run their own G-code interpreter. I would like to start without add-ons that I can't make myself, both for initial cost and repairs later. Thanks.

If you want the cheapest and simplest solution it is likely to be a second-hand PC with a parallel port and a TB6560 board from eBay. Those boards sell for less that you can buy the components for.

Kirk wrote:

So I'm inclined to move away from the parallel port. I think my own amplifier board would be better but if LinuxCNC is not sure to work, that leaves MachineKit, or Grbl so I'll inquire of them, or try a non-cheap KFLOP USB board with built in G-Code that is half of MaxNC's driver board..

LinuxCNC does support many other options than the parallel port. In fact I very rarely recommend the P-port, as it is very limited in performance. However my impression from your enquiries was that you were budget-constrained.

If your criterion is "half the price of the MaxNC board" then options like the Mesa 7i76 set are an option. Or the ethernet version . (though that is still a little less mainstream)
There is also a driver for the Pi and an SPI card , using the Pi SPI interface. That is not in the LinuxCNC mainline yet, but is probably in-budget.

Clearly we have absolutely no way to determine if "your own amplifier board" would be sure to work as you have given no indication what interface you intend to use.