Carrara is great, I've only recently started using it myself. The oceans are amazing. I would suggest the Dreamlight tutorials, they are fantastic and will help you get up to speed faster.

You're absolutely right about the backgrounds, they can be simpler yet still effective. It's the same way with comics - many panels have only solid colors with full detailing only on establishing shots or other important shots.

There is a lot to be said for beautiful matte paintings - but they are not needed in EVERY shot of a film, and especially in conversations between characters you should not notice the backgrounds.