Firstly Id like to say well done on reading up first and figuring out how to use things using search

For your first question (Can there be only one run?) You can level as many characters as you like during the raf period and they will all get the bonus, its an account wide thing rather than character wide.

To get follow bound to the W key all you need to do is go into key bindings on wow (on your slave character), drag the /follow macro onto the action bar then assign the W key to that action bar button.

To accept and complete quests you will want the addon named Jamba. And bind a key in key bindings to interact with target.