Go Aala park for sure. In June, skating it during the day is going to be brutal heat wise but won't be crowded at all. It has lights and gets crowded later.
Just a heads up. Waikiki is tourist central but majority of residence are pretty territorial and do not like foreigners even though tourism is the only thing really bringing in money to Hawaii. It's a completely backward mentality. So don't be surprised if people are rude because you are super white.
You're from up north right? Obviously definitely wear sunscreen.
Do not wear an aloha print shirt.
Not sure what destinations you want to check out but I am pretty sure Oahu has the worst traffic in the U.S. so not renting a car might actually make your stay more enjoyable
Not to be a negative nancy but definitely be weary of the ocean. it's obviously super unpredictable and deceiving. Countless tourists drown every year because of them underestimating the oceans in Hawaii.
Just be cautious and you will have a good time!