Gary,
I'm a humble 981 addict and try answer your questions.
1. You'll get the 2D sonar view at planing speed if your transducer is correctly trimmed.
2. If you cannot get the trim right for planing speed, I would suggest to get a second transducer for 2D view at planing speeds.
3. I think that's depending on the boat / hull type.
4. With a 1197 I don't think that this is necessary, since you can change the views and drive with 2D / SI splitscreen or 2D only. I suppose you have your unit mounted on the dash.
Regards/ Harry