Hello Mary,
Thank you for your fantastic and much appreciated work.
We don't mind if students can browse other courses. Your points are very valid.
On our system, things have been set up with degree programmes as child courses onto which students can enrol. Separate courses making up those degree programmes have been set up as appropriately-linked metacourses. In this way, when a student enrols on a degree programme, they are automatically enrolled onto its associated courses. A diagram of the kind of set up we have is shown in Fig. 3 here:
http://moodle.org/mod/forum/discuss.php?d=181297
When students first register as users of the Moodle site (set up a user account), we would like for there to be one enrolment key (password) which they use in registering to gain access to the whole Moodle site. Once registered, the idea is that students would be trusted to sign up for the (child course) degree programme they were taking; and would have the option of visiting other courses as guests only.
As such, yes, it is a 'single enrolment key as default in all the courses' that I was looking for.
If this is not possible, then I will have to set things up so that only students with university domain email accounts are accepted (I read somewhere that that is possible to do).
With kind thaanks for your advice.
François.