You can add wieght to a model perimeters in a sim.

No, a fast model will not help you for what you want to do. It will help you with reaction time which is helpful

Probably add wieght, reduce power and reduce roll rates.
Maybe a glider, climb then glide and makesure you have plenty of power during banking.

The camera will effect the model as if you added floats.
Not really sure how powerful you motor is.
I had watched people fly electric models with marginal power. Too much AOA and slower speed not generating
enough wind over the control surface .
This will make the controls very sluggish and harder to fly than a faster model.

Also whatever model you use to practice with, add slight down trim becuase the camera will cause drag and will probably
want to piont the nose down.

They get into trouble mostly during banking...becuase not keeping the model at level flight (climb during banking) and barley enough power to pull it
through. The model bascailly just drops out of the sky becuase the wing stopped flying.

I've read articles of how people took pamorama/equrectangular by mounting a camera to a kite. The pano looks pretty cool.