The answer to your question about which after market gauge to select comes down to an esthetic choice, and less of a functional compatibility choice. Most all gauges will work with the K-bike. You'll want to select one (or two) that fulfill your creative needs and that goes with the design. Secondarily you'll look at the electrical compatibility and functionality. Those gauges which actually have good documentation should be preferred -- Dakota Digital, Smiths, Motogadgets, Koso, and so on. Those cheap knock-offs on Ebay will function but good luck if you have a problem, especially given your self-declared lack of skill in the electrical department.
There are some functions that are integrated in the OEM cluster that you will loose when you swap it out -- neutral light, start enable, turn signal auto-shutoff, clock, and low fuel indicator lights. These functions you will have to recreate somehow, or just live without them.
