24v COB rgb 840 strip controled by Raspberry Pi

Can the overvoltage protection be the same component in the example above? I think you have the Gate/Source/Drain on the MOSFET mislabeled. can you double check 

i may be over thinking this, but it looks like i dont need the MOSFET at all. what would the circuit look like without it? 

Correct, only one channel is shown since they are all identical. All the 0V connections will be common together. All the Pi ground connections (GND) will be common together (GND will not be connected to 0V; they are isolated).

Every pin labeled ground on the Pi's header is electrically connected to each other (you can verify with a multimeter set to ohms on an unpowered Pi if you like). It makes no difference if you use a single ground pin, or separate ground pins for the project.

The zener diode protects just the MOSFET. The PC817 protects the Pi by isolating it, since there are zero connections from the Pi that are present on the right side. The GPIO and the Ground from the pi on the left are totally isolated beyond the LED inside the optocoupler.

The labeling on the MOSFET in the sketch above is correct. Without the MOSFET, this can't work. the PC817 does not have the output capability to operate the strip.

You could remove the entirety of the circuit with a 'neopixel' style LED strip as mentioned earlier. The strip you currently have will need the parts shown above, if you want the PC817 isolation.

thanks, what wattage level resistors would you recommend? 

1/4 W is fine for them all, or even 1/8 W.

I only want to have 1 power supply for this Project. Can I use a LM2596 DC-DC Buck Converter to provide power to my 24v LED strip and power to my Raspberry pi.

I think will have to split off the wires from my current supply to feed into the new controlling Circuit powering the Strip before feeding into the buck converter. I would also need to strip a USB-A extension cable so I a viable connection for the USB-A to USB-C cord that connects to my Ras-pi

I'm not sure what complications if any could be involved.

please advise 

I'm making some progress, P817's have not arrived. currently mapping out PCB. double sided. I have a clever way of connecting them all.  White on left is Raspi ground. long white down middle is zero volt.

Blue terminal is location of 817's

The LM2596 modules look a bit risky. It might cause brownout of the Pi 4, or could damage it.

Disclaimer: I've never used that module, so I'm speculating, but I don't get a good feeling about them visually. The feedback isn't universally good: https://www.eevblog.com/forum/reviews/lm2596-dc-dc-step-down-modules-load-testing/

Plus, the Pi 4 has more difficult to achieve supply requirement than a Pi 3B.

It could be better either switching to a Pi 3B, and/or using a board such as these ones:

https://www.pololu.com/category/261/d36v28fx-step-down-voltage-regulators

No need to source a USB cable to strip; the power can be applied to the 5V pin on the 40-way connector on the Pi.

finished circuit, fingers crossed.