I've seen too tight serp belts cause problems on other cars like the 2.5 Ford/Mazda engine. It'll ruin tensioner bearings and cause the crank pulley to separate from the rubber isolator.
I agree, as simple as one would think belts are, there are some out there that just don't cut it (even some
big name brands...)
As far as how tight: you could buy a belt tension gauge for about $300-400.
What I recommend is to start out light and try it, remembering that a new belt will stretch in the first few days. If you don't have to retighten it, it was probably too tight from the beginning. I have seen some guys go so tight on serp belts that they cause the center of the pulley hub to flex and shear.
Beav