As a renter, home improvement can be a little limited.
If you are doing things to upgrade the unit you are in, usually the owner/landlord would be okay with this.
Just make sure to clear it with them before doing anything. I also live in a smaller 17 unit complex and the owner of the building was totally fine with the following projects I did.
Also with the painted walls, I would paint it back to a neutral color when I move out.
Click on the images below for each projects details.