how to develop a new course as a new Assistant Professor
If you believe, as I do, that students learn from practice and feedback, not from seeing or hearing something once or twice, course design focuses on student tasks first. 

First decide what they will do to master the material of the course. Whether that is projects or exercises or exam prep (ugh) or whatever. Lay that out. All key concepts should have reinforcement activities (and feedback from you and the TAs). 

Knowing the student activities you can select learning materials that will be helpful to them in those activities - books, web sites, handouts, whatever. 

Now you have a pretty good idea what your lectures must cover. Note that not everything that you lecture on needs to be covered by exams and projects, but the core of it should be reinforced. If presentation of the core doesn't take up all the time, you can fill it in as you like.