They're too slow, if you run a lot most of the time they will fall back.
They catch up fairly quickly for me. Even if I scaled a mountain.
They don't level up, they are useless later in the game.
Yes they do level up, some cap at different points though.
They wear whatever they want, you should decide what they wear.
Just give them better stuff then there default clothing. The only problem is they take off that equipment when dismissed. Which is only an issue if you want them to walk around town in the stuff.
i think their level depends on what level you were when you first met them, but in the pc you can update them..
It depends on what level you are. Followers are leveled to you up to there cap which varies depending on follower.