Pc Button box

hello people ,

I'm building a 15 toggle switch button box .

12 are 2 posistion on off toggles

3 are 2 posistion 3 pin led toggles

Is it possible to connect all of this to an at mega 32 u4 ?
With the 3 led toggles operating?

If so can anyone point me in the right direction for a wiring diagram and how to program?

Thanks in advance for a complete noob

What is the button box supposed to do with the inputs from the buttons?

I suspect a lot of button box questions are triggered by videos like the one below. The Arduino code makes the button box look like a USB joystick. Many PC games can map the buttons/switches to game features. Button boxes for Xbox and PS4 consoles look like USB keyboards because some games support USB keyboards. Button boxes are mostly used in driving and flying simulators.

Its to be used to control flight sims on pc

What, no extra trim axes?

A button box can be wired as a 3x5 matrix using 8 pins and needing a diode per button to read > 1 button down at a time.

OTOH with 2 input shift registers and 15 resistors you can wire the buttons on the SPI bus that uses 4 pins and can still add more as easily.

A PJRC Teensy 2.0 (PJRC is Arduino friend) has 12 analog inputs and a USB-AVR that can be HID through easy code.
The Arduino Micro and Leonardo do the same but find a Micro that ISN'T a knockoff and the Leo is big and Uno format with pinholes might make changing circuits a bit easier also makes it prone to loosen at every little move or bump.

It's possible to defeat ADC dither in software with these.