You should buy tickets through traveloka, I bought 8 tickets and got a 200K discount. Scanning is fast and convenient, no need to queue.
As for Vinwonder, I think it's normal, the day I went on May 2nd was a bit crowded so I had to wait in line to get a float and play the thrill rides for a long time. It's ok for children to play.
You should go early from 1pm to play until the evening :))
Oh, when you enter the water park, you can rent a locker for an additional 50k, and get 1 ice cream for free.