That Vibrant resonator looks like a great idea. I'd personally be tempted to get the cheaper bottle style, but those are a pretty good deal either way for stainless. From the little I know about the subject, a resonator won't make the system a whole lot quieter, but they do cut down on droning. I've seen a lot of build threads with a straight-flow muffler as a resonator. I'd figure the side-exit exhaust is going to be louder than a rear-exit system regardless.
Are you going to use those slip-joint exhaust clamps? I haven't tried them yet but they look like a really good answer. They will definitely be part of my next exhaust repair.
I haven't used any of those parts, mine is mostly the OEM system with a cheap Magnaflow replacement muffler. I might toss a pair on my E24, it needs a new system.