I'm confused wether I should focus mainly on those or train the entire body as a whole. I think i'll go entire body and hopefully the big chest/wide shoulders will come along with the progress.
You are not listening. At your stage, you need to do like Prince said. Do compound movements. Bench, deadlifts and squats. At this point you don't need to worry about isolation exercises. Take 5-6 years, get some mass and then worry about isolation.