4/
You install "Aurora Store" from "F-Droid". It lets you install non-open-source Android apps. Ones that you cannot live without and cannot "get" any other way.
Again, yes, the FLX1s can also run (many) Android apps.
This is where you would look last, if you cannot find what you want in "Software" or "F-Droid".
I am using FLX1 (not FLX1s). It is a great phone, but uninstalling some android apps (from Aurora store) leaves artifacts that I can't get rid of. Also it is not fully open source. I do have to restart android container often enough for apps to work properly, RAM gets clogged up enough to see messages about os killing various processes. I also stil have screen flickering when power button pressed quickly twice. It is not a perfect phone - but it is my daily driver.