I know everyone is going to start listing a bunch of their favorite actors for this, most of them not looking a thing like the band members or too old to play them young, so I will just say I would honestly go with unknowns, maybe even in some sort of Ireland-wide talent search. Yes, I think they should be Irish. You might need to get two groups of actors, one to play them from the teen years to UF, and a second group to play them from JT on. Oh, the poor Bono one, all the different hairdos he'd have to have! Maybe he can use a bald wig for Pop LOL. I think attention to detail on the 'looks' and clothes should be very important. The soundtrack would be too extensive to list.
I would LOVE to write the screenplay and have actually thought about what I'd say. I would start it off with Larry playing in the Post Office band, and come home complaining he wanted to be in a band with boys his own age. His father could tell him to post the note at school. I would get into a little character development on each teenage boy and his family. I would show Paul McGuiness and his frustration none of his bands amounted to anything, and his idea of a 'baby' band early in the show, though he wouldn't meet them for 2 years, just to lay his storyline.
I would cover all of the ups and downs of their careers, and some of their personal lives, but nothing too nosy or hurtful to them. For example, the story of Bono's mother collapsing at her father's funeral after he had collapsed at his 50th anniversary party would be very dramatic, bone chilling and truth stranger than fiction, and then you could play in the songs like Out of Control and Tommorrow, but I wouldn't want to do that if it would hurt Bono. I'm sure most of the basic facts of their lives must be mentioned, but tactfully. I would do the same for all the parts of their career.
I would end it with the triumphant Elevation tour- unless they have an even more trimphant one before the movie is made!