[Q] Android in the Enterprise and Google Play

I have done some searching but I have a time constraint so I am hoping someone can assist me. We are looking into supporting Android at our facility whether it be employee owned or company purchased. My question is how do you register Google Play to download the MDM app it you do not have or want a gmail account? Or how do I install my custom app on a tablet without an SD card or "Astro File Manager"

I have put the APK file in the Downloads folder but that does not work.

How are you registering devices under a Corporate identity?

Thaks for any assistance.