A good choice
I'm not sure how this applies along the Mississippi, but a 5-weight in 8 1/2' or 9' is a fine all-around choice for trout and panfish. The Cabela Genesis package looks like an excellent value for the beginner, with its included flies and accessories.
A floating line is basic, but in time you'll need a sinking line or a sink-tip, line, and an extra reel or interchangeable spool to hold it. Don't be overwhelmed by the countless thousands of fly patterns; most of them largely duplicate proven standard patterns. A drab color Woolly Bugger will catch fish almost everywhere that's wet. A few Adams or Elkhair Caddis in different sizes will cover your dry fly needs, to start. You've got the rest of your life to expand your fly supply.
I hope you can find someone to teach you basic fly casting, which can be learned in 15-30 minutes. If you teach yourself, use these few principles:
The line will go where the rod tip directs it, so move the rod tip in a straight line backward, which is the wind-up for the forward cast, where you move the rod tip in a straight line forward. Don't thrash the rod as fast as you can; pause momentarily on each stroke to let the line straighten out. Start with a short line, then release a few feet of slack with each stroke; control it with the fingers of your line (weak side) hand. Don't try to cast more line than you can control. You can catch fish by casting 20-30 feet, and you'll get better with practice.
Welcome to the world's greatest sport, which will give you immeasurable joy (mixed with some character-building frustrations) until you're old and gray and bent.