Adobe InDesign or Illustrator at the high end, Powerpoint, Pages, or Google Slides at the low end. I've found Illustrator the best compromise between power and simplicity (provided you have a license).
Likewise. And it's the only way to get decent typesetting on complex equations for one - though it might be a mistake to include those on many posters.
In my lab most of the poster templates were already fairly standard and available on a shared drive. Also anecdotally, I stopped sending my professor LaTeX documents as soon as she said she didn't know how to open them/wouldn't be bothered. It was a point of pride for some professors to use LaTeX, but we generally used word for the edit tracking feature to publish efficiently.
Except for one weekly in-person lecture (and the project-related material) cs230 consisted of deep learning.ai Coursera modules, so videos and code are on coursera.
How advanced are those student in their studies when they take this course?
Their work is probably good but I can't help but think many of the reports/posters seem underwhelming. I doubt they would be accepted at the universities I know.
http://cs230.stanford.edu/projects_spring_2018/posters/82658...
http://cs230.stanford.edu/projects_spring_2018/posters/82857...
http://cs230.stanford.edu/projects_spring_2018/posters/82845...