According to [this source][1], the speed of a sailing boat depended on the waterline length.

The exact formula quoted there is `hull speed = 1.34 * sqrt(waterline length)`

A boat with a waterline length of 50 feet would therefor go about 9.34 knots (~17.3 km/h or ~10.75 mph). This of course only applies on open sea with good wind.

I have not found any sources for the maximum speed on a river, but I guess it's safe to say that it would be half the speed, at best.

[Those guys][2] discussed something similar, and came up with an average travelling speed of 5 knots (~9.26 km/h or ~5.75 mph) for a trading ship with a waterline length of 75 feet. That would, of course, change depending on wind conditions, the river (Does it run straight or in a lot of turns?) and your direction on the river (Upriver, downriver). But I have no Idea how the exact modifiers are for this.

As for the rest of your questions, I have no idea and hope that someone else here can help you. Take this as a general direction, not a fully fleshed out answer. ;-)


  [1]: http://wiki.answers.com/Q/What_is_the_speed_of_a_medieval_sailing_ship
  [2]: http://forum.rpg.net/showthread.php?466330-Travel-times-of-a-laden-medieval-merchant-ship-no-coconut