Bit late to the party, but I'd like to play
Whoever plays R should be fairly young, not just because of his age in the books, but because a Jack movie really has a strong chance of sparking a series of movies. I suppose it'd be possible to change actors for Rasalom, but it'd be much better if you could keep the same actor over the course of (potentially) a dozen movies.
I like the idea of Benedict Cummerbatch or Luke Evans but the ethnicity/look probably isn't quite right. Cummerbatch crossed with Javier Bardem would be perfect in my mind but I'm drawing a blank on a current actor who looks just right.
Wrong place, but I'd go with Liam Neeson for Glaeken and Joseph Gordon-Levitt for Jack (or maybe Michael Fassbender).