rasberry pi 2second boot to GUI

We require someone to be able to create a custom Rom file we can flash an SD card with. Here is our goal: We require the rasberry Pi to load instantly to a Pyqt Gui we will be building in the near future. The device will be used as kiosk that people will turn on over and over again. The pi must be capable of shutting down safely just as fast within 1 or 2 seconds. During boot up, our goal is to instantly launch into our Gui interface with pyqt, while it can quickly load in the background usb, and dhcp, services. We will also need it to be able to run our 4g hat. We may also use sleepy pi just so we can use an external start button.