... I'm wondering ... do you mean "I haven't done any studies on plate tectonics" as in "... yet", or as in "... and intend to skip that" ?

Because if you are going to think about tectonics after mountain placement and river placement, it's much harder.

If you aren't doing tectonics, then I guess those mountains are as good as any other. But, even without tectonics, I think your continents are too evenly spread out - it will look more natural if you don't try to have such a "democratic" distribution of space and importance.