Where will the Raspberry pi go? For this, there are two solutions : over the electronics, or under it.
If going over, we'll have to make another stage to the robot. It will cause it to have another piece to print, but it makes it easier to upgrade afterwards. You build the basic robot, and if you want, you add another layer with extra stuff.
The second solution is to have it go under the electronics board. In that case, i'd use a 2*20 connector, so that the electronics board would plug directly onto the pi, that would go in it's current position. The plus side is that it's easy to connect the two boards. It is the solution i chose for R.Hasika, as this other robot has a Raspi in all cases. Here, the raspi is optionnal, so we'll have to figure this solution out.
Furthermore, we want to keep costs as low as possible, so we opt for the Pi Zero as a primary solution, so we can think about optimizing space while maintaining easy maintenance, hacking and configuration.
In all cases, i plan on making it possible to use each model of Raspberry pi form factor (B+/2/3, A+, Zero), so two or three tray models.
I think that the pi zero and the A+ make the most sense (low power and cheaper) for this robot, but i want to provide options to users. Anyway, i'll start with the zero tray, then the A+, and finish with the B+ format.
See you soon :)