Purchase rules and rebooking

We are arriving in Japan on 17/12/23 and we plan to activate the 14 day pass on arrival with an activation date of 23/12/23.

Am I correct in the following:
If we purchase the pass after 18/09/23 but before the end of September, we will get in before the price rise and be compliant with the conditions of the pass?

Also is it possible to prebook seats prior to activating the pass - reason I ask is we are travelling during the busy period before New Years.
Thank you