For internal wiring of a kit 24AWG-18AWG is fine. The differences heard in various wires come down to many factors but are typically a product of the metal used, the insulation, and shielding or geometry. Bigger isn't always better.
Try to remember the effects of wire on a given system are very subjective and tend to be quite subtle. Adding a little high quality wire to your kit may bring some positive effects but generally won't make a huge difference. Of course I encourage you to experiment and listen for yourself. Just don't expect a miraculous change. Also, keep in mind that not everyone hears exactly the same due to varying levels of damage to one's hearing.
In all honesty there's a great deal of debate out there when it comes to wires. Many consider the science of the subject case closed while others feel we haven't figured out how to measure everything yet. I try to keep an open mind. But then it was hearing the difference between 2 cables that got me into this hobby. So I'm a little biased.
