> - We are told the Atreides ruled Caladan, but at no point is the audience shown who the Atreides' subjects are...
I'm not sure why this is particularly needed and it isn't really in the novel. The importance of Caladan in the novel is that it is wet (which we do see); and that the way Caladan is ruled (whatever that is) must necessarily be different than how Arrakis is ruled (air/sea versus desert power). I'll have to rewatch the film to see if this can be gleaned from it; but it seems largely irrelevant what day-to-day life is like for Caladanians not in the Duke's direct employ and if the Duke is particularly loved or hated there.
> - On Arrakis, we are only ever told how strong and powerful the Fremen are...
This is also true of the novel. The main characters know more about the Fremen than anyone and very little at that. The Duke believes the Fremen are his 'desert power' because of the comparison to the Sardaukar on Selusa Secundus and because their estimates of the number of Fremen are greater than those of the Harkonnen or Emperor. Duncan Idaho confirms these suspicions, but the Fremen are largely mysterious even then. We also have the interaction between the Shadout Mapes and Jessica to hint at their capacity for violence.