The most important rule about the future is that You Aren't Gonna Need It. If the future is known then it is called "requirements". Design is for protecting you from the unknown future: allowing code to be changed in arbitrary, unforeseen ways.
As for coupling and cohesion: if modules are too small, they usually lack cohesion ; if module are too big, they usually have high internal coupling. The sweet spot is in the middle. And you can create low-cohesion, high-coupling modules if you want :-)
As for coupling and cohesion: if modules are too small, they usually lack cohesion ; if module are too big, they usually have high internal coupling. The sweet spot is in the middle. And you can create low-cohesion, high-coupling modules if you want :-)