Combat rule question

[MwaO]

Iron Fist or Whirling Defense. When I hit with a melee weapon I still add my Strength mod to damage and the feat adds psionic damage as well, correct?

No. Whatever the power tells you do, that's what you do. Only with the default melee basic attack or a power gained from str-based class do you do +strength modifier.

So Iron Fist does 1w+Constitution. If you were using a Rapier and had an 18 Constitution(+4 modifier) and no other options, you'd do 1d8+4 damage unaugmented. If you augmented it by 2 points, you'd do 2d8+4 damage.

(edit: and the damage would be untyped, not psionic)