It's time to slow down and take a deep breath here. I actually have one of these machines (Concept 55) on the shelf that I've done nothing with yet, but have looked into a controls retrofit for it.
Let's start with the servos you bought. The only advantage they have over the very high quality original 3 phase steppers is that they have encoders attached and are somewhat better documented for the hobby user. Adding linear magnetic scales would accomplish the same thing and work better. The original steppers and drives are quite robust.
Mesa vs. Sain smart boards. Not even in the same universe. The Mesa products are a few orders of magnitude better. You already have a computer power supply to run the controls and boards.
A single 48V linear power supply would be my choice to power the motors. This one would run all 3 motors https://www.automationtechnologiesin...0vac-or-230vac
The torque of the original spindle motor is about all the machine will take, it is a small machine and not rigid enough to take high spindle loads. It would benefit from higher spindle speeds than the original. But the spindle bearings need to be considered when increasing the speed, I'm sure they would live at 6000 RPM, but not much more. Maybe later replacing the spindle motor with a 1KW servo motor would be a possibility and give you enough torque and control for rigid tapping. Thread milling is really a better option in most cases.
Slotted raceway, available in many sizes. https://www.amazon.com/Raceway-Manag...ronics&sr=1-10
Din Rail normally available in lengths to 1 meter https://www.amazon.com/WatchfulEyE-P...ronics&sr=1-10
Also Automation Direct may become your new friend. https://www.automationdirect.com/adc/home/home They have everything you could possible need for panel building, normally my go to vendor. Not the least expensive, but great service and support when needed along with consistently high quality products..