Well, all I can say is, don't assume this is the last bike you will ever buy. That puts a huge amount of pressure on yourself.

Eventually you'll get to a point where you learn your body and your style and figure out what works best for you, but that takes a bit of time. Sooner or later you might "outgrow" your first road bike and sell it, or better yet hang on to it as your commuter or rainy day bike, and get another bike that suits you better.