A bit late to the thread.
Yes, there are better ways than flying indoors.
To go back to your initial questions, for real estate you probably don't need the new features of the P4 and the P3 Advanced would do just fine.
It has the same camera as the P3 Pro and the P4 camera is also the same with a minor tweak in the lens.
I'd be cautious about the Autel machine if you want straight lines to look straight in your photos.
Beyond the Phantom sized machines, your next stop is the Inspire with the X5 camera but that a huge step up in cost and in portability.
In aerial photography everything is a compromise but the Phantoms are a good compromise.