Definitely get navy first. If you search for "black suits", you'll get many heated discussions, but the prevailing opinion will be to just don't do that.
You didn't write where you are located, but take a look at the recommendations above (Suitsupply and the suit quality thread for options). How fast do you need your suit? It is always risky to recommend a new operation like that when there is no previous experience. IMHO, a safer and faster option would be to just get a decent RTW first, especially if you are not a difficult body type to fit - you can see what you are getting. Once you already have your first suit, you will be in better position to experiment with custom operations like that.