Hi Cham, regarding the VG's, I have them on the bottom leading edge elevator. They work great. Highly recommend. They really do help to give more elevator authority at slow speeds, especially during landing when you need it. During cruise, the VG's are hidden behind the horizontal stabalizer.
I wish you the all the best with your project. If you ever get the chance to visit the Zenith factory please take the time to stop by our builder assist facility too. We are their newest and nearest builder assist facility and like to have visitors. We are right here in Mexico, Mo., not far from the factory.
Developed specifically for Zenith builders (by a builder) these videos on DVD are a great help in building your own kit plane by providing practical hands-on construction information. Visit HomebuiltHelp.com for the latest DVD titles.