Creaking is very minimum. I only noticed when I hit a big bump, no more than with soft top. As for shims, I didn't get any shims with the top but I did have to raise the hinge up about 1/8 of an inch on both side so that the hatch door could cleared the top when opened. I really like this Zeintop and it really give you the best of both world (convertible/coupe).
From the pictures, it looks like you did a great job fitting the zeintop on your car. The seams fit pretty well. I wish the the soft top had a similar curvature when they were designing the Boxster, that would of been a pretty sick look for a convertible top...feasible who knows. Definitely a nice transformation for a Boxster. Great job!