Well, MicroG is meant to be a drop-in replacement for closed-source Google libraries on your phone (i.e. Google Play Services / Google Services Framework) but obviously it will still have to connect to Google servers if needed (although you're able to control for what purposes). For instance, push notifications for apps often use Google's Firebase Cloud Messaging platform and MicroG allows the user to still receive those notifications in the absense of Google Play Services / Google Services Framework.
I suggest you have a closer look at the MicroG website where this is explained, too: https://microg.org/
Do you want fastest/easiest? I may be opinionated but try JHipster. If you want a Kotlin version try KHipster. Full Stack + Open source + all bells and whistles loded
May be or may not be. The unpredictability makes everyone curious to understand . I believe there must be a beginning but i'm not to sure about the end.