Welcome to the club--speaking as a Mac user with experience dating back to 1986 and who also deals with PCs on a daily basis at work, I'll wager you won't be disappointed. Heck, as soon as you see that cinema display plugged into the G5 sitting on your desk, every worry should fade away very, very quickly (sure wish I could afford a new display).
I also think you made a good call going top of the line for longevity's sake--that's the same thing I try do do now, and it's not just for bragging rights (though that's funn for a little while, too). Just shy of three years ago, for example, I decided to spend the extra cash on a DP533 G4. I dumped a bunch of RAM and some fast hard drives into it, but it's otherwise unadulterated, and surprisingly enough it's still quite snappy and a fine computer today, even though I push it quite hard (lot of DV video work). Although it looked like a lot of money at the time, my investment has more than paid off, and is considerably cheaper than if I had bought a midrange model then and one more in between.
Actually, my trusty G4 easily has another year of life for me, but the DP G5's siren call proved too much temptation, so I have one on order now, too.
Besides, with a new G5 you get the added bonus of the thing getting faster over time as more is optimized for it.
Don't read too much into the Rev A business--there are always issues, but the first G5s to trickle out are looking quite solid, and there have only been a few quirky Rev A models anyway.