Longer wires just means the spark has further to travel. Not a major problem unless it gets in the way of something moving or gets to close to a heat source.
As far as getting a coil wire, you should get one in the kit. Sounds like you got a "returned" set or one that was missing the coil wire. I would order a set from Summit Racing -- they're sure to know what you need, based on your vehicle or your engine. I've been very happy with my Taylor wires and they were actually cheaper than purchasing them from a local parts store.