Scalable UI, best target device (Android)

I have a small question regarding scalable UI’s. I am developing an Android game with widgets which as of now are not scalable. But I have the documentation in front of me. I am just wondering what target device (Phone) is nowadays recommended to make a scalable UI for the best results on all phone devices?

If It helps, the entire game is in portrait mode

And an extra question: Is it recommended to make a seperate UI to toggle between to for tablet devices and if so, which tablet is recommended as target device?