@First 2 questions: Monte Cook addresses this with "GM Discretion". The foci and different paths available are ready to use, but also serve as guidelines for players to make their own stuff (subject to GM supervision/discretion, of course)
The creation process can be as in-depth or bare bones as you want it to be.
Cool thing: if you want to shoot lightning from your hands. you dont necessarily have to explain  how it works. The mystery is part of the fun. Do you have latent magical pontential or a colony of bizarre super-scifi nanites coursing through your veins? you can pick either and neither is wrong, because numenera is that open.

As for the feeling of diversity.... I played the numenera-equivalent of a devout priest who prayed to the great machine sprites and did ritualistic sacrifice of cyphers to get visions of the future. i also had a combat yo-yo with monofilament garotte wire... 

So go nuts xD