I am not sure if the T200 will be able to reach the speeds required for a foil board. @adam may explain.
That wireless controller looks perfect, but I am not sure if it will work. You need to know what PWM the controller centers at, and where forward/reverse end. If you use one of the ESCs from our store, neutral will be at 1500 pwm, full forward at 1900 and full reverse at 1100. Most other ESCs will only operate in one direction, ~1100 is neutral, and ~1900 is full throttle.
If you use 2 T200s side by side, then you will need to control them individually with two channels and a ‘steering’ mechanism on the controller. You probably cannot wire them in parallel to one channel, because minute differences will cause them to push different amounts of water, and you would have a bit of a turning motion as you try to move straight.
Regarding a power switch, you will need something capable of handling the current draw, probably something rated at at least 80A for 2 T200s. You could go without a switch (for a limited period of time), the electronics will draw an amp or so when idle, much less than when operating.