You cannot just download the Play Store app alone; it acts as a framework that relies on other Google services. For a successful installation on a device without any Google apps, it is highly recommended to use the method, which bundles the necessary dependencies.
To install the Google Play Store on a device running (often referred to as "portable" for handheld or specialized hardware), you must manually side-load the APK file along with its required system frameworks. 1. Enable Unknown Sources google play store apk for android 810 portable