The idea of Luke NOT joining up with the rest of the friends/rebels/alliance opens an interesting space for a possible future edit of episode VII ;-)

He would have taken the same path as old Ben maybe to learn in solistice (again), finding new recruits and rebuilding the Jedi order ... or ?

And on the other hand we would have the Galaxy still in turmoil (Rebel-) Alliance against the (remains of the) Empire - but what "secrets" could the former "Galactic" Empire hold ? (not to step unto more EU territory)

Well, too bad so many things what could have been and too few that really were (like the PTs) ...

As for the force ghosts - Ben & Yoda should stay as "old friends" Luke left behind (party or not) - Anakin finally released as spirit at his "funeral" is a nice touch, not sure if not better to show Shaw version though