I don't know if it is a good idea to ask these questions here but,
I am planning to design more than one pcb's which sizes and pinouts are the same with rapsberry pi 3 and connect them all together. For example pcb1 will use 3 pins on pi, and pcb2 will use other 2 pins on pi. pcb 1 is on top of the pi, think that pi's i/o pins are long enough, and pcb2 will be on the pcb1 and so on.
It will be something like that http://www.harrowalsh.de/Elektronik/APPLEBOX/Gameport/web/16GameportIOPiggypack_plugedinLeftside.jpg
My questions are,
1) is it a good idea to do that? what is your recommendations?
2) i will change the raspberry pi gpio pins with the long ones. but which connector can i use in the other pcb's?
3) do you have an another idea to connect 2-3-4 small pcb modules to pi? think that these pcb modules are selectable for users. In one design, user can use pcb2&pcb3 and pcb2&pcb4 in another design.