I would think you'd need two control rods about that length for your rudder and elevator (17 1/2). They're very close to one another. The two shorter ones are for the ailerons. Then there should be one about 10-12 inches long for the throttle.

That crack in the covering and wood: Is that in the cosmetic balsa nose that goes on both sides of the engine? If it's minor some CA will do it. If it's bigger a little sheet of balsa CA'd on the inside will hold it good. You can iron on a small piece of covering if it's a solid color. If it doesn't bother you, you can CA the covering too (I've done it plenty of times on my beater trainer).

Repairs are pretty easy with a balsa trainer. If it doesn't bother you, fix it. If you're really picky, send it back.

Joe