I think there might be one other guy on here with that type of experience. I would be a close second. I never worked in the duct shop but I was in the field for three years installing duct so I know how the shop works. I've done takeoffs for the fab shop, piece by piece, knowing exactly what they need. I know the fitting codes, S/D or TDC connections, FOB, FOT, throat size, in. w.g., etc. I've been using AutoCAD MEP since 2007 so I'm very familiar with the program you're now learning.
The best advice I can give you, is to post up what you are trying to accomplish, and I can do my best to tell you how to reach your goal. Since I'm from the same type of business I'll understand what you're trying to do and I know AutoCAD MEP pretty well as we have a long (and difficult) history, haha.