Not that I want to push you into the nearly-bottomless pit that is tectonics. But if you start deciding altitude and then try to make it fit tectonic movements you are just creating yourself a problem. It's better to decide right now than to throw away hours of perfectly good work .

Again, not pushing into working the tectonics out, but would you give me permission to use a part of your land mask to write a little tutorial on the subject? I want to use some virgin (as in without tectonics worked out) world map and I prefer something people are actually creating.