We are also doing Japan next summer (July). We plan on going 4 days to Tokyo Disney after
ABD. We want to stay on property which is hard to get. It appears that the package trip might be easier for the main booking so we hope to do 2 day package (the most you can do) which has 3 park days and then pick up another hotel only the first night and then the 4th night. Hopefully all on property. If you hope to stay on property make sure you understand the booking process since it is so different that WDW.