I had to wait almost a full month to get mine. (end of March)
It was worth the wait. Honestly I wouldn't buy the add on discs just yet. There is some cool stuff on them to be sure but you don't "need" them right now. The money I spent on #1 and #3 wasn't a waste but it would have been better spent on something else.
I'm running Windows 2000 with a pretty low end video card and had zero problems. Just stay away from the ATI cards and you should be fine.
I can't say enough good things about G2. I spend at least a full hour a day flying on it. There aren't many planes I can't fly and land safely. The jets are kinda tough but I make it more often than not. Not to say that it's easy but with a LOT of practice you get more and more confidence.
Go ahead and order it now. Spend another couple of days asking questions and deciding which plane you want to start with. G2 should get to you hopefully before you finish building the plane. Then you can do a ton of crashing on the computer instead of with your plane. I can't speak with the experience of the others here. All I can say is what is working great for me. Good luck.