Minimalist Manta Ray

Is this happening consistently? If so, my guess would be that maybe the CS pin is shorting somewhere (or getting sent incorrect inputs?) which causes the outputs to go into a high impedance state. If not, then maybe try swapping out that RAM chip to make sure that it's not a bad IC.

Has he tried using the buttons attached to the contol board to switch between inputs? Usually these control boards don't auto detect the input and it has to be manually selected.

Yeah it seems some people have used it to draw power from a charger or power bank as shown in the video, but make sure that the USB port on your MacBook allow you to draw that kind of power (I'm not sure but I think they are limited to about 15W). Do update if you get it working.

I agree. While not optimal, some MOSFETs can be switched directly with an Arduino. Using a MOSFET driver is certainly better in most cases.

You could use the transistors to switch your relays. They won't be able to switch the LED strips directly, but you can use an NPN transistor or even a Darlington pair to easily switch on and off the relay, just make sure to use a flyback diode. +1. Using a MOSFET would also allow you to control the brightness of the LEDs using pwm signals.

USB-PD is designed to supply upto 20V/5A(100W). However, the available power is offered at 4 different levels- 7.5W, >15W, >27W, >45W. The available voltages for each level can be checked from this graph- Also, in order to select the amount of power you want to draw, USB-PD requires the two connected devices to communicate to each other(a "handshake" has to be made to select the appropriate power/voltage level). Since your display requires 12V(and probably around 2A, as most displays do), you would have to build a logic circuit to communicate with your MacBook via the same USB cable and then hook it to a buck/boost converter to regulate the voltage to 12V. ^Both of these are meant to supply power TO the MacBook and not draw power FROM it, hence these only supply the required power and won't allow you to draw power from the USB port. If you want to design your own circuit to handshake with your device, I would recommend starting here and here. If not, I too would say to go with a 12V adapter or a battery to power your display, it would add a bit of hassle but is a much simpler solution.

Instead of the second screen underneath the first one, I'd rather have a solid physical keyboard. Kinda like the Blackberry Torch(but swivel instead of slide/fold still makes lesser sense imo).