There is a whole noticeboard about brushless motors etc on this very forum. You'll find far more on there than I can put in one post, but to answer your queries very briefly:
1. Low-speed control is much better than it used to be, even with sensorless motors. That said, you are building a Riva speedboat - not a tug.
2. Outrunners have more torque and don't run at such loony speeds as inrunners, so they tend to be the preferred option for our scale model boats. 'Fast electrics' are a law unto themselves.
3. A brushless motor will always run at the "calculated" speed i.e. Volts x kv when the full voltage is applied. It will just take more current to do so the more you load it up (with a larger prop), but you have a proportional ESC anyway. Just don't push the throttle stick so far, or reduce the travel on that channel (if you have a computer radio). If you find it's
much too fast then reduce the number of cells in the pack.
BTW you don't
have to use LiPo batteries if you don't want to; NiMH cells are fine, but don't even think about SLA bricks.
Here's a short video which Martin D took of my little 1/16 scale (24") Huntsman at Wicksteed. There's some low-speed reversing round about 45-50 seconds in. The power train is as described in my previous post, using a 3S LiPo battery (11.1v) and 32mm 3-blade bronze prop.
https://www.youtube.com/watch?v=uw1C8SfZPS4&feature=youtu.beDM