First, I would say that if you're happy with the price, then just do it!
Most of the specialty restaurant slots will likely be booked, as will the "adult beverage" tastings. For kids, the princess and pirate makeovers may be booked up. The more popular excursions may also be sold out.
However, if you don't mind checking the app each morning, before bed, and when you're bored at work (haha), then reservations may pop up.
On embarkation day, you can go to the specialty restaurants to inquire about availability (I think reservations are often held back).
However, the bookable character meet and greets, such as the princess gathering, only open up at the start of check in. That's at 30 days, so you'll have an equal shot at that!
You will definitely be placed in the later dinner (which we enjoyed, even with a child), but there's always a chance you can be moved to early dinner depending on availability (if you want).
Again, for a four day cruise, I would totally do it even if I couldn't book anything. I haven't been on the Wish, but it seems like there's already too many things to see and do that are included with the just the standard cruise fare.