‘Excellent news, but do we have any idea about potential cast members??’
I expect that they will start signing contracts and announcing cast members almost immediately. It is expected that the cast members from TLOTR who were in the Hobbit will repeat (Gandalf, Elrond, Gollum, Galadriel). Bilbo is much too old, and Saruman probably is too (he wasn’t in the book, but it is expected that the White Council will be included in the movies). Speculation has included nearly every English speaking actor in the world. Go to “ http://www.theonering.net/ “ for discussions.
Not necessarily. One of the first things Gandalf says to Bilbo at the beginning of Fellowship is, "You haven't aged a day". It's my understanding that from the time Bilbo found the One Ring, his aging slowed, because of the power bestowed on the one who possesses it. So whatever Bilbo looked like at the beginning of Fellowship is what he would look like in The Hobbit. I could understand, though, if Jackson wants to go with someone a little younger than Ian Holm; it certainly wouldn't make me enjoy the movie any less.