Let's say that you max out your level. All your major skills are fully developed and you're not leveling anymore. Are you still able to develop minor skills, or does all character development just stop at that point? Thanks.

Why of course! It won't help you with any attributes unless you go to jail for a few days and level up some more.

There are also mods that let you develop skills far, far above 100, with bonuses, too.