Getting enough tall people to play Wookiees really could not have been that big of a hurdle. I’m sure some basketball players could have filled the bill. And Peter Mayhew could have taught them all how to act like a proper Wookiee. 😃
In any case, casting a large number of little people wasn’t all that simple either. There was a maximum height for an Ewok. In the Classic Creatures doc it’s mentioned some were told for the first time in their lives they were too tall for the part!
In the Star Wars To Jedi doc, Lucas explains that when he wanted to revisit his idea of primitives defeating a technologically superior foe, Chewbacca had already been well established as a sophisticated creature, which led him to “short Wookiees”.
He also said in the end, “Dare to be cute.” 😉