Just to reinforce what JJ said, rstudio.cloud is currently limited to 1GB of memory and does not have access to a GPU.
If that is sufficient for what you need to accomplish in the class, wonderful. You could look into creating a public project that the students could copy that contains the files and installed R packages, rather than having them upload the same zip-file, or using a Space to organize the students and their projects. The number of students is not an issue.
While we expect to make the option of more memory and a GPU available in the future, I would strongly suggest running through the coursework to ensure that it stays within the memory limit, otherwise the students will have a subpar experience.
Hope that helps.