I bought my kit with the decision to enjoy the build as much or more than the finish, and I got frustrated too. You should enjoy the build man, because when it's working, if you are like me, you will miss the days when you were still building it.
I actually destroyed my cranbrook hub by over tightening in an inexperienced attempt to make the coasterbrake into a fixed gear. Now I have a mountain bike hub with a few gears to choose from and a free wheel. I could add a derailer, but I don't think the cruiser frame was made to harness a derailer and it's not that important anyway.
Honestly, I think I have exceeded 40 mph on my old fixie, that's without an engine. Too bad it got stolen in front of Boarders in down town San Diego :-( I had pegs on my fixie, rather unique, I'd rather not peddle all the time. As a matter of fact, I think I will build another fixed gear bicycle, to ride in addition to my motorized cranbrook, I am getting kind of fat these days