Moodle HQ offers a twice yearly MOOC on Teaching with Moodle on the LearnMoodle site
You might find a presentation by Gavin Henrick here useful - Using Moodle for MOOCS and there was a paper published last year (on an earlier version of the MOOC here: Our MOOC with Moodle)
We used a custom theme but there doesn't seem to be any specific theme. I'm sure others will suggest plugins that have been used in MOOCs to make the process easier. On ours, we tried to keep plugins to the minimum so as to demonstrate standard Moodle, as that was the point of the MOOC.