This demo shows how to create a tablet app with the basic 3-screens you normally get when using the phone format (with 'Start from Data'). We definitely hear your asks related to Start from Data, in that you'd like the option to start in tablet format too. This is planned, but not expected immediately as of 1/2018. So, until we release that option, these tips will help you to get your tablet apps started more quickly!
Give it a go! I timed it (without me talking as much), and the steps take about 5 minutes to do - start to finish!
Resources:
https://docs.microsoft.com/en-us/powerapps/working-with-form-layout
https://docs.microsoft.com/en-us/powerapps/run-app-client
https://docs.microsoft.com/en-us/powerapps/set-aspect-ratio-portrait-landscape
