One of the observations of Mahara is you can't disable Login easily and that I used as a launchpad to Moodle not all the requires fields are there. The solution I used was to make Moodle the only login point and the by placing the Network server Block on the login front page learners can then do a simple jump. To make things more interesting there are several other back end Moodles also on SSO (MNet), the advantage is that Mahara is available from all Moodles and the learner ID is preserved, as well as, backend Moodles can use the Portfolio.
It's been the bane that we over multi Moodle/Mahara sites need to preserve and transfer the student intact. So to speak.
On the mahara side I replaced 2 files the register.php and lostpass.php with custom files that redirect to the Moodle login or register. Because I am lazy I left the Mahara Login box, need to fiddle with the themes to do that.
To make the whole thing a little more rounded I use a WP machine as a launch pad. Sorta MOOCS in a slightly structured way.