Jim-
There is a great list of aerobatic schools sorted by state on the International Aerobatic Club (IAC) Web site (http://www.iac.org/begin/schools.html). I'm pretty sure that a couple of those schools are in your area. There's also lots of other good info on that Web site.I'm pretty much of a beginner myself, but if I could start in either a Citabria or a Decathlon, I'd go with the Decathlon, especially if the price difference is small. From what I hear, it does aerobatics better than a Citabria, but not nearly as well as a Pitts, Extra, or other high-performance aerobatic airplane. I bet you will still have to work to get the maneuvers right!
The Citabria (7KCAB) I've flown had a 150 HP engine, and I think many Decathlons have a 180 HP engine (? I have also heard of 110 HP Citabrias and 150 HP Decathlons, so go figure). A significant difference is the constant-speed prop on the Decathlon, which will mean fewer power changes in mid-maneuver.
On the inverted systems, I think you will see a benefit to having inverted systems very quickly. It's not like you'll be doing outside loops on your first lesson or anything, but you could conceivably be practicing level inverted flight early on. It seems to me that, even with the beginning maneuvers like slow rolls and 1/2 cuban eights, it would be a distraction to learn them in an airplane without inverted systems. You could do it, but why not just go for the Decathlon?
Whatever you choose, have fun!
Tom P.