My dream cast for Uncle Andrew is slightly impossible, but I think that Daniel Day-Lewis could be AMAZING as this character. He's a terrific actor, may I even say the best of them all, and I have no doubts that he would give us an interesting proposal for Uncle Andrew, but not sure if he would be up to it... I bet he's too busy. Anyway, I think that Paul Giamatti or J. K. Simmons could be great choices as well, they're both astounding in what they do.
Daniel Day-Lewis would be a perfect choice for the role, though not sure he would take on a movie like this. He does movies once in a blue moon and puts his entire life into the character as he is a method actor. He certainly has the look. They would need an incredible supporting cast other wise it would look like one professional actor playing with community theatre try-hards.
I don't have any recommendations but do hope they keep the kids at the same age as they are in the books which I guess is around 10 to 12 years old. Hollywood likes to add romance where it is not needed and can't imagine they would want to throw away an opportunity for some romance in the story. So many easy ways for the story to be ruined in a movie adaptation.