So, I was able to place level convertion circuit to protect Raspberry Pi from 5volt arduinos. And some LEDs to help with keyboard usage. It would be great to be able to see feedback from using Raspberry completely without a screen. For example you can program some script to be launched using the hotkey and a result can be displayed via LED. For example: Ctrl+U+1 to upload some code to Arduino and blink green led once if success.
P.S. Probably will need to refactor again, to add 5v-3.3v switch for Arduino pins.