So I eventually managed the
Amazon Fire (Xda) method...partly... I can now access the Playstore "sign in", but it will stay forever at the "signing in...this can take a few minutes" screen.
It may be related to the third app installed, GoogleServicesFramework.apk , which gave back "Failure [INSTALL_FAILED_OLDER_SDK]" I can see the app in the file manager, it's version 6.6.03. I suppose I should find an older version adapted to 4.4.2. but I'm not sure where to find it or if I should use ADB to downgrade GSF.apk..
I regularly get at each boot "GplayServices has stopped", and I get "com.google.process.gapps has stopped" when I enter PlayStore's Sign in portal. Anyone's got a clue ? Thanks...