Well, there are only two LFS here, and one of them only opened a couple months ago, so we don't have too many choices in Tucson. Southwest Saltwater (now on Oracle) is where I've shopped for the last 10 years. But a friend of mine opened up Simply Elegant Aquatics (on Campbell) and that store is really nice as well.
Most people put the powerheads in the back of the tank. In a 55, the back would be better. Is your tank drilled? Or are you using an overflow box? Most people use PVC as their plumbing.