Hello, and welcome here.
I can't answer all your queries, since I've given up trying to make the Cosmo work as a genuine phone, but I will say you're not alone with your CODI woes. IMO, CODI is essentially junk and there aren't too many users here that will disagree. I had the same faulty listing of contacts (CODI would only generate a partial listing) that you suffer and I never solved it.
Nor do I know of many users that use Gemian as their daily driver, but there are some. I now use my Cosmo as a Linux-only laptop and am pleased to do so--I do not use a SIM card with it.
Some of your display issues may be tied to the rooted aspect of your setup and perhaps others will weigh in with their experience. One thing I did use right away, and also use it with my Pixel 4a, is Nova Launcher (in the Playstore) and if I remember correctly, that will solve your 3. dilemma.
I know I was able to set myself up as Developer, some sort of tapping 7 times or something, but it can be done (though perhaps not in root, now that I think about it).
The Cosmo can function as a daily driver, it just takes work and a lowering of expectations and God knows you know your stuff (your setup is airtight) so you'll find your way, though not with CODI
![Smiley :)](https://www.oesf.org/forum/Smileys/default/smiley.gif)
Again, welcome,
Jake