Congrats on your new job! You are going to love sixth grade.
I just came from sixth grade where I taught Reading, Writing, and Social Studies. A few tips I found worked for me:
I like your idea of splitting your day as if you were in middle school...then the topics and activities will change every hour or so, so the kiddos won't get bored and act up. I would think of something you could do with them to show that it's time to transition from one subject to another, as well..we used to use a bathroom break for that
I required students to have one giant zippered binder, and the separated that binder out into all then subjects they had, each subject with it's own folder. That way, there was never a "I forgot that binder in my locker.." conversation, they always had the right notebook.
A good rule of thumb is that kids need to move or change activities about every 1/2 hour. I would advise NOT having them sit and take notes for endless stretched of time..try to incorporate some centers (we called them stations) or games to get them moving around and talking to each other.
I used to spend the first 3 days of school introducing EVERY routine: how do I walk to the pencil sharpener, what does silent reading look like, how do I take out a class library book, how do I move my chair away from my desk, etc....a few days of prep work makes a big difference throughout the year.
As far as decorating, that's totally personal choice...I've seen 6th grade rooms that carry themes, and ones that are just organized and colorful. I tend not to go with a theme becuase I think it's too elementary, but some teachers love the idea. Whatever works for you.
That's what comes to mind at the moment. 6th graders are awesome, they crave independence and responsibility but are just learning what to do with it when they get it, and they love to move and talk....organize your days around those basic concepts and you'll be great!