to answer question one, i'd wait personally.
if pioneer are advertising a new rekordbox then it must be due soon. re-gridding a big library is a large task and if the auto beat grid detection gets improved then it will be a massive waste of a lot of time.
regarding your second question, just go for what suits you best. there's so many different ways to organise your music with rekordbox. i also use the 2 sd card method if it's any help.