I am unsure of what you mean by the GET function. If you are referring to making GET requests to another server, then yes, your cron scripts can do that. If you are referring to PHP's $_GET variable, the no as the script is being executed from a command line (cli) environment instead of from the web server
You are allowed to have 1 cron job every 5 minutes. This means that if you have multiple cron jobs, you need to make sure that they are all at least 5 minutes apart from each other (so if you have a daily job and an hourly job, you should schedule the daily one at 12:05 or 12:10 so that there aren't two jobs running at 12:00). If you break this rule, the offending crons will be silently terminated and deleted.
