Unrelated, but I feel it's unfair to rob the word "bookkeeper" of its peculiarity of having three subsequent double letters by inserting a space in the middle.
The existing "linux phones" are much worse for general use than AOSP (putting aside that AOSP doesn't run on any device by itself and looking at projects like grapheneos and lineageos instead). If Google decided to fully close off Anddoid (which would presumably violate some licenses somewhere, though I'm not really familiar with the situation), then conceivably the existing AOSP would be a better starting point. In any case, people tend to complain that each new Android update brings fewer and fewer significant changes; maybe only security patches and driver updates would be needed.
Google Play Services is independent of Android releases and will update itself automatically, though I believe you can disable this by uninstalling a specific system app with adb.