buy logitech smart hub or similar device, it will allow you to use single remote for all devices and can start them in proper sequence (like: TV, then AVR, then RPi), you can also add delays between these devices if needed.
in my case single button on the remote starts the sequence which is switching on TV, AVR, RPi and then switching the pilot to mixed AVR/Kodi mode - volume buttons work for AVR, while other buttons work for Kodi, the whole startup sequence takes around 15-20 secs.