Willdo, doesn't it make most sense to try at the recommended CG? You can put some lead weight on the tail and remove it as you become more familiar/comfortable with the plane. Many people start with self-adhesive lead weights to test the plane. When they find the amount of lead they are comfortable with, they replace the lead weights with a more permanent solution. But then, if you are installing a stihl and moving back firewalls, you should've already known that :-)

As for getting someone with more flying experience, that is usually a good call if you're not completely comfortable with the plane yet.