If the full MPP kicks in, you would get 4 extra modules so you will need to look for an extra case, power supply and a cgminer running CPU (rPi, PC, laptop) with a USB connector for each module
Besides, the MPP modules will only ship out in 2014, you'll get your bought expansion board in December
This isn't right.
It doesn't max out Raspi, it maxes out space. Remember the cool thing about the modules is that they daisy chain together. This is why in the Sierra you can string 3 modules together with 1USB feed to an external controller of your choice.
Sure, it maxes out space, cooling and power supply in the (beefed up) BabyJet, but it will also push the rPi to it's limits so that is why HF in PM recommends:
So we recommend something more powerful for one or more Sierras.