You could solder a usb port, or just plug a micro usb to usb adapter and plug into the pi itself.

Alternatively you can use a program like putty to remotely connect to the pi if needed and eliminates the need for a keyboard.

That screen you posted is totally normal. You have to configure controls when starting emulation station for the first time. Since that board you are using utilizes gpio controls you would need to install retrogame and configure it based on the gpios you used. Here's a link to with retrogame install...

Here it is , I think everything is alright. Looks to be wired to the correct area. You could try cleaning up that red wire a bit. It doesn't look great. But if the measure voltage is not 5v it's likely not the issue, I'd try another boost module if you have easy access to one. I ordered an adafruit...

Here it is, I think everything is alright.

Looks to be wired to the correct area. You could try cleaning up that red wire a bit. It doesn't look great. But if the measure voltage is not 5v it's likely not the issue, I'd try another boost module if you have easy access to one.

I connected the battery and still nothing . Then, I measured the voltage of the output and it reads 2,36 v, this is probably the first thing I should've done but I'm still a noob. Should I get a different powerboost? Do you have a battery connected? If not, connect the battery to the power boost. I...

And also, if the pi is stuck on the boot screen rainbow, re flash the SD card and try again.

Does it stay on the rainbow screen, or cycle through it? If it's cycling it may not be getting enough power to boot. Check the power supply you are using.

Do you have a battery connected? If not, connect the battery to the power boost. If I recall correctly that power boost needs the battery connected to function properly.

Also, measure the voltage on the output of the power boost, see if it is providing 5v.

Double check all the soldered connections between the gpio of the pi and the DPI board. Some of them don't look great.

Also ensure you have a properly formatted SD card with an image that has the DPI drivers installed.

When connected to power do you see the LED on the pi at all?

No. But there are alternatives for the SP. See here:

https://github.com/Gameboypi/SPW

Do you have any pictures it is salvageable likely.

Alternatively you can cut a micro usb cord, and plug it into the pi's usb, and solder the data wires (white and green) to the AIO