I can't say I know much of anything about the "correct" placement of mountains. They usually come at plate boundaries, either in the form of upheaval or volcanic activity...but there are lots of exceptions, I think. I can suggest, however, that a good way to make them is using Ascension's atlas-style tutorial. There's another tutorial about making realistic mountains that involves hand-painting if you don't like that style. I like the outline of your landmasses...no complaints from me there.
M