Thank you everyone for the feedback on this topic. I'll try to address some of your questions and comments below:
as far as print size is concerned, I currently print 8x10 on paper and I often use 100% crops of some of the images for screensaver/background images. In the future I would not imagine printing past 16x20. I crop significantly due to the fact that most of the insects that I have available to me are really tiny and I want to showcase some details that I may find interesting.
I agree the 5D3 is probably one of the best overall DSLRs on the market at the moment and even though I "only" had the 24-70L f/2.8 on it, I was very impressed with the image quality, I found it virtually noise free up to ISO3200, minimal noise at 6400 and at higher ISO speeds it will let me walk away with a very good possibly usable picture.
on my current setup (rebel XT, 100L f/2.
, I've conducted experiments and I have noticed that for certain subjects (fabrics, rusted metal, etc) I can take pictures at f/22 without noticing much change. for insects or flowers with smaller details, I do notice a slight loss of sharpness at f/16 and by f/22 I have lost a fair amount of detail already.
I have not played around with focus stacking, although like LetTheRightLensIn mentioned below, I may not be able to apply it to moving subjects. I haven't dealt with extension tubes either.
distant wildlife... yeah that is a whole other dilemma, last winter I found myself needing ISO1600 to get decent shutter speeds for early morning ducks needless to say I had a lot of noise issues there.
I suspect my next step is to head into one of the big stores here in NYC and play around with some of the equipment. I'm still keeping an eye out on the upcoming rumors as I am interested to see what the new APS-C "semi-pro" body will feature. I'm not shooting professionally yet so I am not in a big hurry to buy something.