Re: What Items to Purchase
It depends on the kind of Calligraphy you want to do.
I would expect you want to draw fine lines for outlining your drawings. A pointed pen (nib) would work well for that. Try the Zebra, Nikko or Tachikawa G nibs. These are fairly stiff in terms of flex and very easy to use. More flexible nibs like the Hunt 101 or 22 are finer and produce wider swells useful for Copperplate or Ornamental Penmanship but require a very light touch.
You will need a holder for the nibs. Straight holder are usually $2-$3 a piece. Nibs are also in the same price range but get a few as they do wear out and are considered consumables.
As for ink, you can try Sumi which is pigmented and some varieties dry waterproof. India ink is also pigmented and waterproof. Walnut ink (available as crystals or in liquid form) is also very good but might not be useful for outlining paintings.
BTW - water colours and/or gouaches can be used as 'ink' too when diluted to the consistency of milk. It can be applied to the nib using a brush.
This is only very general information. Please feel free to ask for clarification where needed.
Those who say it can't be done should get out of the way of those doing it.