I don't know at what point the elements from "The Searchers" came into it (you are clearly better versed in the minutiae of Lucasiana than I am) but I think in the final product it's pretty obvious - we've gone over this before elsewhere, but I got sh!t else to do today.

A lot of the first part of the movie is taken right out of "The Searchers." The landscape of Tatooine looks just like John Ford's beloved Monument Valley panoramas (minus certain distinctive rock formations like "The Mittens," the Sandpeople raiders are analogous to the Comanche raiders, Luke loses a father figure (who's not really his father) in an early raid while he's away from his home, like Martin Pawley - and discovers the burned homestead in a nearly identical shot. He spends the rest of the movie searching for a kidnapped female relative (nice bit of slight variation here - in The Searchers, the girl isn't his sister, although he feels like she is - in Star Wars, the girl is his sister, although he doesn't know it.) And niftily, Martin Pawley is 1/8 Comanche while Luke is 1/2 Darth Vader. I think it's even arguable that the Comanche ambush of the posse is a bit like the raid on the Death Star, especially when they pilots fly into the canyon on their way to the target compared to when the posses get surrounded and make a break for the river.

Anyway, if you can't tell, I recently rewatched "The Searchers" and it still whoops ass.