Note: If you are going to start building your cockpit for the first time you should remember that it could be a very complex and long process, especially if you make a wrong decision choosing one of the "heavy metal" planes with tons of complex systems, controls and custom data.
You need to know much about many aviation-related things, and preferably you should have various technical skills, at least some craftmanship ability and basic experience in wiring and soldering.
To reproduce all tech solutions presented here and use SimVimCockpit you should understand all possible risks and carefully learn all aspects of using electric and electronic equipment.
Don't turn it into an "endless" process for yourself, trying to make a "real big bird", select a plane cockpit that you really can build in a couple of months.
Then, you can start configuring your controls and outputs. Open SimVim configurator, find a parameter that you think is the most appropriate for the selected control, display or annunciator, and assign it to the direct input pin, multiplexer input or output pin acccording to your connection diagram.
SimVim Interface architecture allows you to have only one master controller board, plus input extension breackout boards, additional slave servo and stepper controller boards (Arduino Uno, Nano, Mini). Also the key-matrix input slave board is planned. For all input extensions, output (7-segment displays) extension and LCD/OLED one common 4-wire address bus is used.
If you need, this architecture is suitable for modularity - for every input "module" you can use a 6-8-pin socket jack to connect it to the address bus.
But think, why would you need to have separate detachable "modules" in your cockpit? My opinion is quite opposite - the best way is to make all in place, using soldering instead of multiple connectors, carefully planning all the wiring first, of course.
I don't think you will have several cockpits in your house, but even if you will, you don't need to make a removable switch panel and carry it between two cockpits, right?
It's more reasonable to make well organised wiring in each cockpit. You should plan your whole cockpit design before wiring, clearly realizing where every switch, group of switches, displays and annunciator groups will be located. This is not mass production, you do not need to think about universality and try to make some "unified" modules, PCBs (especially!), or connectors.
. Try to optimize input wiring (switches, buttons, encoders), groupping them and placing multiplexers right near of this group.Example: