Prerequisites were self-enforced. There was only one case were someone took the workshop and was probably not qualified, but he seemed to manage anyway. Part of this was due to people arriving last and part was do to the complexity of the process. Making the setup process as simple and comprehensive as possible is recommended. If the workshop is hands on, it's good to provide skeleton code with notes.
Students can then start working on the relevant parts of the program.
Many students did not have CAEN accounts or had CAEN accounts, but they didn't work. I let people without accounts use my account. These people created a directory in my directory and worked out of that. Any setup script should allow the user to specify which directory is used. Count on at least two CAEN computers being broken.