VERY, VERY good ideas here ! Do DJI have a "request" box somewhere ?Digital zoom (post cropping) editing is best. Record in 4K and crop back to 1080p.
To assist, use an A4 transparent overhead projector sheet and create a mask or box that is roughly 1/4 of your smartphone/device and then centre the mask. This will help with cropping and getting the subject matter in your footage. The mask will speed up cropping as you don't need to tell the editing software where to crop frame by frame.
DJI should have created a 1080p mask on the GO app (similar to the grid and diagonal lines) or have on-the-fly enabled 4K crop at 1080p mode.