Love the idea of making one! I would join. But as far as already established communities, the http://www.diymobileaudio.com/ forum is by far the best place. Really knowledgeable people and they are really nice. They’ve helped with a few of my projects.
To answer your question, I would like to ask if you are specifically looking for a head unit running android, or just a head unit with a screen and can use android auto with your phone. If it is the latter then I would recommend kenwood or an alpine unit. If you have any questions about the specific model lmk. We can talk further based on your needs 👍
RF are kinda mid and overpriced imo.
It all depends on your budget/power/space requirements but generally my go to’s are JL Audio, DC Audio, Sundown, and best bang for your buck is by far NVX.
DC/Sundown if you want some seriously loud bass (SPL). JL Audio is also a bit overpriced but you can find used W4/W6 all day for really good prices and I think they have the best mix of power and sound quality. I am personally running two NVX 8” in a ported enclosure in the spare wheel compartment in my vw alltrack off of a 500w rms amp and they get crazy loud for being only 8” and I have them tuned to about 30-32hz and they get pretty damn low and sound very good. I would recommend NVX all day, but if you can get a good price I would probably still get some JL Audio subs. Can’t go wrong with either though as long as you match it with the right size amp and box.