Keynote template for classroom course

You can do all that with any of the basic templates. As I said originally I would suggest keeping it simple and use say the WHITE theme. Personally, I find using a BLANK slide easiest as I can add images/diagrams of any suitable size/shape and easily add a text block with my own font and font size.

The actual content is something we probably cannot assist with - only YOU know the needs of your audience.

I'm not a guy nor am I a classroom teacher. I would generally choose a white or similar distraction-free template as my starting point.

You will need to provide more information such as do the students all have iPads so will you be considering using Keynote Live? If so you will need to look into how transitions and animations are 'handled' and other limitations.

How large is the room? Consider size of 'type' and clarity of the information.

If this is your first presentation and you believe you MAY need to stop and start the presentation and go back to previous slides my suggestion would be to use a simple display method where the forward and back arrow keys move from slide to slide. ALSO use your own Mac as make the presentation so you do not need to deal with fonts or other content not being available.