I had a similar sized IG pool growing up with a single light. Works just fine. There are areas that are lighter than others, but it's all a little light. Certainly enough. If you are looking for a pool that has a uniform brightness -- use more, but most people don't care that much.
Ask yourself how often you'll use it after the 'cool I have a new pool and I can swing [EDIT: ahem ... "swim"] at night' feelings are gone... then decide if it's worth the extra $$