You need to know what you are trying to accomplish before those questions can be answered.

How much is this world like earth? Do you care about enhancing the believability of your world to the kind of reader who understands something of geology, or are the laws of this world so different that these things shouldn't be expected to work the same way. Or is it a lighter, more humorous world where believability is not a goal?

Also some of these things are more obvious to more people than others. Few might notice that you didn't take tectonic plates into account, but many people might notice a rivers doing impossible things.