Once you built the moduls (DIN, DOUT, AINSER) you can connect almost everything directly to these modules without using anything “extra”. Everything important is already on the midibox modules. Take a look at the different module descriptions on ucapps.de, there is always some kind of example schematic of how to connect hardware elements.
Just make sure you´re using the right module for the right component (DIN for encoders and buttons, AINSER for faders an pots, DOUT for leds, MF_NG for motorfaders, …).
So, yes, a breadboard can be easily used for Midibox development.