I didn't expect such a complete discussion. lol
I want to thank off of you for your answers.
The reason I was going to practice indoors is because even though this winter has been fairly uneventful here, the wind still kicks up, and it still gets too cold. The sporstplex is more like an airplane hangar, and all walls are protected by high nets, and I have permission to use it when it's empty, which is more than I can say about a lot of the outdoor areas near me, so I though it would a good place to just practice 'getting the feel' of the controls in a protected location. I won't attempt to RTH.
I had a couple of Parrot A.R. drones in the past, and although they were more like toys and had lots of trouble fighting a small breeze, but they taught me to be sensitive to the fact that flying needs to be done right! So I want to verify my abilities with the Phantom 3S before risking losing it.
Again thank you all for a spirited discussion.