Pierre Massat wrote:
I also saw that the board could power LEDs. This could be very interesting,
Yes, but the Digital Input are "shared" with the digital outputs. So if you put a button on a line, you cannot put a led too. You have up to 12 inputs/outputs IN TOTAL. You choose in your program if you want something to be a input or an output.
Given your questions (no offense), I would go with a Mega board and not bother with multiplexing yet. That way you get a fully assembled, ready-to-use 50 inputs/outputs for your leds and buttons, + 16 analog inputs, with plenty of program space.