Can anyone tell me if there are different songs in the stage version, and if the characters are different?

Everything is different down to the last detail. Most notable are that ALL the characters, though they sing most of the same songs, have very different personalities on stage.

Also, in the film, Tommy is a religious figure, a sort of avatar of Eastern religion who symbolizes and perhaps slightly parodies the rush for non-Western spiritual awakening of the Sixties and Seventies. In the stage show, Tommy is a media darling, part rock star, part magician and part motivational speaker, whose fame and success balloons out of his control.

One big difference is that the Show reverts to the idea of the original album by having The Lover killed and the Father surviving.

Yeah, they change the personalities, most visibly with Uncle Ernie. They decided they didn't want to have it be over-the-top wacky like Keith Moon's performance, so there's that.

I think the most radical difference is with Sally Simpson and the ending. In the film, everyone decides they're fed up with what Tommy wants them to do. In the stage, Tommy realizes that his cult is going out of control and basically tells them to shove off.

Also, the stage version omits the commercial song, the Holiday Camp song at the beginning, and "Rain Champagne." It also adds in a new song called "I Believe My Own Eyes," whiiich really doesn't sound like anything The Who would perform.

I've always felt the stage version had an incomplete arc because they went from Tommy's cult of personality starting to Tommy ending it in basically a couple of montages. I felt they didn't explore the guilt of the parents enough, and also like they didn't set up Nora's lover as a replacement dad well enough that his death could have had such a traumatic effect on Tommy. Also, on a more nit-picky fan note, I loved Tommy's battle with the Champ in the film, and the extended instrumentals in "Acid Queen" and other numbers.

For some time, I've considering constructing a new stage script that is basically rooted in the changes the original Broadway version made, but incorporating material from the film to pad out the plot a bit and make it more palatable. Oh yeah, plot-related bone to pick with "Acid Queen"... it went from Tommy's head being messed with, to Tommy's dad contemplating letting the Gypsy give Tommy a fix and deciding against it. I think this comes from the early Nineties' heel face turn on the Sixties' "experiment with everything" ethos, and in tandem with incorporating the film's extended instrumental, I'd have Tommy actually subjected to the acid.