Hi Ben
You are correct in your assumptions. Joomdle originated from the desire to leverage Joomla front end design (templates) and numerous extensions while providing Moodles course management. With that in mind, Joomdle integrates to the most logical Joomla components extending the functions that Moodle sites could otherwise struggle with eg. solid e-commerce features, mailing, forum, memberships, etc.
With regards to design, you can pretty much choose any Joomla template and many choose to use the most basic Moodle theme disabling the Moodle navigation altogether for students. That said, design considerations are still important (perhaps more important) because you need to fit the course content nicely into your Joomla template design. Example, if you use Joomla left and right module positions and your course is full width, then you are likely to have width problems. Thus most ppl would not implement right side modules on course pages. It is important to note, however, that not all Moodle functions have been replicated. Joomdle only addresses students and not teachers or administrators who require much more navigational options for creating courses, etc. Also, students still engage with courses in Moodle although it appears as though they are in Joomla.
I hope I have addressed your questions. Let us know if we can be of further assistance.
