Some shorter tours to learn are not a bad idea, but... They are not an absolute necessity. You can do a long tour as a first tour if that works for you. Three of us did a coast to coast with no real touring experience, but a lot of camping experience. It worked out very well.
Short tours and long tours are an entirely different thing. You may like one and not the other. I love to be on the road, but tours of less than a week just aren't that much fun to me. I'd rather do day rides than do a weekend tour. My point is that you should keep an open mind if you try a short tour and don't like it much. You may still like the cross country type experience.