A bigger screen is nice but you are making a more unwieldy less portable set up.
You do need a reasonable amount of RAM to run the app and play the live video feed smoothly so don't expect a bargain basement or older used one to necessarily be up to the job.
I would see if the samsung is OK before buying anything else.
The app will need internet initially as you need to log-in to a DJI account, you can download maps for planned flying area on wifi at home and they are cached though not indefinitely in full detail.