Jan
I too like the way a brushed small quad can do a return to home. I have mine set at 12 m/s and I like to fly it high and far away till it's just a dot. Then do a return to home and have is stop just in front of me at the home WP. It's a crowd pleaser.
With your Kisssy expansion board the easiest way to go would be to use the four connection to control your four ESCs.
To use the Kisssy expansion board you need to have the firmware for external ESCs.
The four connection on the expansion board are for ports 5 thru 8.
You can use the firmware wizard to easily find the right firmware.
To use a 2s lipo I would buy a BEC that would give 5 volts to power the M4 when connected to the VUSB connection on the M4 board.
You must also connect a wire from the 2s lipo to the ADC connection so the M4 can adjust the motors thrust to the voltage level of the lipo.
Here's a link to a recent build that's similar to yours.
viewtopic.php?f=40&t=4632&p=34638#p34638Larry