Nobody can tell you what the seas will be like. Chances are they'll be just fine, but oceans are oceans. Some days the water moves around more than others. The Diamond is a big ship with perfectly good stabilizers and can handle ocean motion pretty well.
Not sure what kind of problem you would expect to have with a room near the elevators. On modern ships noise is seldom a problem unless you're on one of those spring break drunk cruises, and you're not. Basically, being near the elevators just means a shorter walk to the elevators.
Any geographic features that you absolutely don't want to miss should be seen from on deck. It's easier just to run up there than to try to figure out where they'll be relative to your balcony.