[Son of Númenor]

I think your answer to the second question answers the first as well. Obviously, Christopher Lee wanted to be in the movies, and who would turn down such a talented actor with such devotion to the material? It became apparent to Peter Jackson at some point during casting, if indeed it wasn't apparent from the start, that Lee's credentials, appearance and acting style made him far better suited to play Saruman than Gandalf. McKellen has a warmer demeanour and a seemingly humbler disposition than Lee, who is the master of playing the Cold, Well-Spoken & Cunning Villain. (Well, actually, he shares the honour with Jeremy Irons.) Although it is interesting to note that another actor originally chosen to play Gandalf was done away with a few days into shooting, McKellen was the obvious best choice (in the opinion of the majority, if I may speak on their behalf).