We have done it, but really we were not able to do/see everything we wanted to. Also, it can really depend on the crowd level. The busier they are, the more difficult it will be to see everything.
As for which park to visit first depends on what you are most interested in seeing. If HP is important to you, I would definitely do IOA first, and head straight there when park opens. It can get crazy fast. I think if I were you I would research the attractions at both, and prioritize what you want. Then choose based on which park has more/higher priorities for you.