I like the casting, but I'd go with Lane Smith as Big Jim.
Although probably a bit too old, when I read UTD, I pictured David Spade as Junior. John Goodman would be perfect for Big Jim, and as for Barrrrbie, that's a tough call.
Ray McKinnon as Pastor Coggins, he played the Reverend in Season 1 of Deadwood, and was an amazing character.
This is the cast I sort of envisioned in my read. Quite a bit different than most peoples, but here it is.
Big Jim … Gregg Henry / Ian McShane
Junior … Ryan Kwanten / Ben Foster
Barbie … (No Name)
Rusty … Callum Keith Rennie
Julia … Natalie Portman
Carter … Keanu Reeves / Jeremy Renner
Andy Sanders … William Sanderson / William H. Macy
Cox … Brian Cox
Burpee … Garret Dillahunt
A bit late in my response, but since I just finished the novel here are some of my ideas.
Big Jim- Phillip Seymour Hoffman... he may be a bit young, but I like John Goodman and Hoffman seems like he can play someone even more morally corrupt than John Goodman
Here are my choices for the Under the Dome Cast.
Big Jim- Phillip Seymour Hoffman (maybe a bit young, but I can never see John Goodman as the bad guy)
Barbie- Timothy Olyphant (remember he is supposed to be in his early-thirties 10+ years younger than Julia)
Julia- I like Rachel Weisz for this
Junior-I like Ben Foster or Joe Anderson as well
Andy Sanders- William H Macy would be perfect
The Chef- though he maybe too old I think Jackie Earle Hayley would be perfect
Carter-?.. maybe Dax Shepard?
Rusty- Damien Lewis
Nice kaskramstad...Jack Earl Haley is one of my favorite actors since Watchmen...I'm going to watch the new Nightmare on Elm Street on Halloween as a tribute to himThe Chef- though he maybe too old I think Jackie Earle Hayley would be perfect
My twopence worth,
"Big" Jim Rennie - Paul Sorvino
"Junior" Rennie - Logan Lerman
Carter Thibodeau - Domhnall Gleeson
"Chef" Bushey - Lucas Black
Sammy Bushey - Sarah Bolger
Julia Shumway - Emily Perkins
Joe McClatchey - Freddie Highmore
Oh, and M. Emmet Walsh as Big Jim