Good luck with your planning. Definitely a good idea to get some redemptions in before you are tied to school hols. We are tied to school hols now and I am having to book tickets 11 months out to try and get MFUs (and often still not succeeding).

Tokyo is a very interesting place to visit but it is very spread out if you want to see some of the temples, Mount Fuji etc. Will be hard work with a 2 year old I think. I'm taking our 10 year old next month and even then I think we'll have to pace ourselves. Hong Kong, as others have suggested, is much more compact and probably more do-able for you with a small child.

You have done well to get 800k miles in 6 months so enjoy them.