(1) Imagine the following case: It's your turn, you played the paddle card "4" and your canoe is one river disc away from a discovery place.
Am I right, that you cannot move one river disc further, load a gem from the discovery place and skip the last "movement point", because you must use up all "movement points" and you cannot load inmidst your move?
Correct. You must use all your movement points, and loading gems must occur at the beginning or end of your move, but cannot split up movement of your canoe on the water.
(2) If I have BOTH canoes at the docks, I am nevertheless allowed to play the cloud card, right? I ask because of the rule, that you always have to put at least one canoe into play.
Not sure of this one. I'd allow it. After all, by not putting a canoe in the water, you're really only hurting yourself.