I will add a little more to what both Howard and Melanie have said.
#2) Moodle is one of the most robust LMSs when it comes to importing questions. I regularly import questions from textbook publishers.
#3) Limited the time a quiz is available is easily done with Moodle. You can limit the quiz within dates and times, you can limit the quiz to a certain number of minutes, you can limit the number of attempts, and you can easily provide student exceptions.
#1) Enabling/disabling a user with a batch job, I am guessing, will take some special knowledge of your server and the moodle database. I have never had the need to do this. I am not exactly sure what you are seeking. You might need to explain your need a little better. For example, do you mean "add a batch of students" or "suspend a batch of students?"