Congratulations!
For your classroom set up, since you have very little time up front, think about your flow and organization. You can leave the walls mostly blank, since most of the stuff will be teaching charts or student work and you can add them/change them as you go along.
Think about how you want them to sit the first few days for organizing the student desks/tables. Consider how you want students to enter and know where to sit the first day. Think about where you want student work to be turned in. Think about if they are going to have some sort of task at entry and if you need materials for them to pick up as they enter, where those would go. Think about if they need coat/bag storage while in class. Think about if you want them to use a common heading on their paper....routines and rituals.
Focus your time on the procedures and rules you want to introduce and enforce beginning on day 1. Make sure they correlate with any school, district, and state policies. Hopefully your school is large enough that you are not the only math/science teacher on the grade. Seek out people who can be a good source of advice and support throughout the year.
Familiarize yourself with the curriculum and your state standards/benchmarks. Create a road map overview for your course content for the school year. (This can probably be done over the weekend from home, if your school does not already have a curriculum pacing guide.)
Oh, and take pictures of the classroom when you first walk in, then what it looks like ready for the first day. Take some more as the year goes along....and in following years. I can't believe the difference between my first year classroom and this one (my 6th year)!