I've only had AL teams until a recent mid-season pickup of a NL team that I plan to hold onto for a while, so this is all theory, but I would think that you need a stronger bench in the NL due to pinch hitting, as well as some multiple position players on the bench to allow for double switches.  I would think you'd need reliever that can give you more innings in the NL as well since you'll have starters that might be pulled a bit earlier due to pinch hitting selectiveness while in the AL that same pitcher might go another extra inning or 2.

W/ my AL teams, I've had success with multiple relievers that can give you an inning at most, the 10-15 pitch count type guys that can't pitch 3 days in a row.  I don't intend to have more than 1 of those on my NL team.