can you reduce the number of caps?
how to boards like the rbbb, or the boarduino get away without all the caps?
The 7805 regulator requires 2 caps minimum. Leave off the 7805 and say goodbye to 2.
Cin is required if regulator is located an appreciable distance from power supply filter.CO is not needed for stability; however, it does improve transient response. Values of less than 0.1 uF could cause instability.
It's set up so you can use either a crystal or an oscillator. A lot of people don't care either way, but a lot of people do. I figure it's better to give the option.