Hi Kjjames.. welcome to 4th grade! and welcome to teaching! This is the best ever place to ask as many questions as you want! We all help each other.
Advice for the 1st day: Yes, def teach expectations and rules. I have my kids work in groups of 4 or 5 and write on a large chart how they can be kind, a different group lists ways they can be responsible, etc. I tell them I'm watching to see how they collaborate. Then we discuss them and make a chart out of the best ideas. When walking in the halls, insist on quiet. Choose a secret walker i got this idea here. Tell them you are watching the secret walker and onlyl you know who it is. If he/she is a quiet walker in the hall all day, he/she will get a prize at the end of day (piece of candy)
Model all day long how you expect them to move from activity to activity and hae them do it over if its not perfect. Read them a story and have them write a response to it. Give them a focus question (How did so and so change from the beg of the story to the end?) and tell them to write a full page. (4th graders should be able to do that) This will help you see how they write. Teach expectations but remember to teach content also. Keep them busy all day.. No down time. Good luck,, I'm sure others will give more advice. 4th graders love stickers and stamps and still like the teachers to like them

)