A few questions from a first time install

I'm installing a 2-stage heat pump/air handler and ran into a few uncertainties today... they are probably basic but I thought I would just dump them in one thread to get it all over with:

1) When unbrazing, my oxy-acetyl torch has a hard time getting the fittings hot enough. I am using a #0 tip and I assume that's the problem. What tip would you guys use on 3/4" copper?

2) My old ducting doesn't quite match up with the new air handler. Can I just make some block off plates out of sheet metal to mate the duct to the handler? The sizes are close but not exactly there.

3) The aluminum fins on the coil in my air handler were delivered with some smashed spots. Is that normal? ie, should I ask Goodman to send me a new coil? There are a few spots about the size of a half dollar and I straightened them out the best I could but they are still not spot on.

4) My old air handler was growing quite a bit of mold on the inside. It is in a crawlspace that gets humid sometimes. Is there way to prevent mold from growing? I read a trane bulletin stating that UV lights don't do much.

Thanks!