If you are going opening weekend and only going one day I might avoid Friday... we went the first day a couple years ago and there were some snags (late characters, things not well organized)... we went again the following Sunday and it seemed like they had things better organized and I don't think it was any more crowded than Friday.
That would be said I would HIGHLY recommend going if you have a SW fan... one day will probably be enough for most things; however, if you want to meet *every* character and do everything than it would probably take more. Also, all the Star Wars stuff ends in the late afternoon so if you have park hoppers you can go to MK or Epcot after it is over for the day.
As far as what to do... unless you REALLY want to meet the celebs I would skip that... you need to be there insanely early and spend a lot of time waiting. The main things we did were meeting the characters, the parade, and hyperspace hoopla... all of which are great... we didn't bother with the presentations which are mostly question/answer with various stars or sneak peaks/behind the scenes stuff which make not be that interesting to and 8 year old (but I could be wrong about that)