Is there a re-encounter with the sea monster that ate Shanks's arm?
Yes, Luffy did. It isn't shown in the anime, but Luffy reencounters this Sea King, the Lord of the Coast, later in chapter one of the manga. Immediately after setting out from Foosha village Luffy is attacked by the Sea King, and is pleased to have a chance to show it what he has learned in the ten years since their last encounter.