Awesome write up and installation! 3D printing is becoming a game changer in many different ways.
I am not personally sold on headunits which require a phone at all times. I assume the answer is to purchase mobile mapping SW which includes maps stored locally. Google Maps caching could be a short term solution as well, as long as one remembers to sync the map area in which you will be driving, before heading out on the drive.
Standalone vs 'smarter' headunits is a matter of personal opinion of course. Your installation is great and offering the iPhone ashtray replacement holders for order is fabulous. Thank you for your contributions to the TT-RS community!