Feed the Mega from 5 volt into its 5 volt pin.
I could make this change, however, there is one other VL53L1X distance sensor not pictured in the circuit (sorry!) that will be connected to the 5V pin (plus ground, sda, scl) on the arduino. So, I though I would 'pad' the voltage by using the 12V - 9V regulator.
From what I can see, there are 2 ground loops. The ground from the Mega to the Stepper Motor Driver Shield and the wire labelled "Ground back to Arduino". If these were removed, everything will have a separate ground path back to the Power Bus terminals.
I ran this by another formum on adafruit - I questioned this second ground from the LED back to the arduino. It was suggested on that forum due to the potential noise encountered back through the ground through 5V voltage regualtor. I would like to know if this second ground could cause an issue over what it is purported to solve.
Buck regulator specifications can be, er, optimistic, so save yourself some headache and be conservative on loading. Buy real ones, not eBay &c.
I believe each of three regulators provide 2x the amps anything could draw — thanks for this reminder, I will be sure to check current draw and voltage coming from these regulators. They weren't the cheapest regulators available on Amazon, but they're definitely on the low-end.
I would hope that the "shield" would, um, serve also as a shield against any motor issues.
Yep, it has protections built right into the shield.
How far apart are the 4 non-power blocks?
Use appropriate gauge wires.
All of these components (minus motor and lights) are secured to an ~8 in square panel so the power lines are all less than 10". I probably use higher gauge wires than needed, perhaps I should pay more attention to the resistance in my wires/connections — how can that effect things if you may know?
That's weird way to wire the capacitor on you LED strip.
Ha, I, errr, was going from icon-memory when drawing this