I agree that having a good rotation at NT is very important for this defense to be successful, but I'd say a SOLB and a FS with good cover skills are our two biggest defensive needs (fortunately the draft is deep at these two positions), with a backup NT for our rotation right behind them. Though with so much emphasis put on our defense the past few drafts I would like them to start putting focus on adding youth to our offense, especially on the line and at WR.
My point before was that a good NT prospect isn't going to just fall to us wherever we pick - we're going to have to trade up to take one, and that means we would have to reach when what we really need to be doing is adding picks and taking the BPA.