That drawing of Leia (presumably by Alex Tavoularis) is featured in the book The Cinema of George Lucas, where it’s (likely mis-) labeled as being by Ralph McQuarrie. I’d say it’s from around the time of the third draft, which is when Leia was reintroduced after being almost entirely cut out of Draft 2.

I agree that Alec Guinness’ gesture of removing his hood adds much to the feeling of Ben Kenobi as a wise old wizard. I wonder if that was improvised? It’s amazing how much GL could get out of his actors simply by letting them do their stuff.

Also, here’s another Mollo drawing of Ben Kenobi’s original Tatooine outfit.

And just for good measure, here are some drawings by Ralph McQuarrie for Ben’s Jedi robes. The rightmost drawing, showing a set of fancy blue robes, was apparently meant as a ceremonial outfit for Ben to wear during the medal ceremony at the end of the film (before GL decided to kill off Obi-wan on the Death Star).

Incidentally, blue and white seem to have been intended as the colors of the Rebellion during pre-production on the first SW film. Several John Mollo sketches of Rebel soldiers show them wearing blue jumpsuits and white armor plates.