My best recommendation is to rent a car. You will need a way to get to and from the airport anyhow, and having a car to explore the island at your leisure or leave Ko Olina for a meal or groceries was really convenient and valuable for us. Ko Olina is a small, planned gated tourist community, so you really don't get much of a sense of true Hawaii unless you go out and explore, and having a car is the most efficient and flexible way to do this.
As for the resort, we loved Ama Ama breakfast and the spa. Beach chairs never quite reached capacity so they were easier to come by than pool chairs. Not sure what the pool chair situation will look like with the pool closure and construction in September, but in our experience, the chairs in front of Ama Ama had availability later on in the morning as well.