A DCTank is a tank that has cartomizer in it. The "D" stands for dual, as in dual coil. The cartomizers come in both single and dual coil. Both work in the DCTank. Most of the time a simple eGo type battery is not sufficient to get the most out of a dual coil, at least it didn't for me.
The cartomizer either has a flange on the bottom or not, hence flanged and unflanged. The flange only allows you to insert it one way into the tank. Sometines the flange has flats that make it fit a certian way.
The number of holes punched determines how much liquid flows into the cartomizer. this is subjective, different liquids and what material is in the carto, plus the user preferance will determine size and amount of holes. More research and trial and error is needed to make a decision on what you'll require.