Getting the Journal to 100% is a tough but achievable challenge for Crops, it will take a lot of time, but is quite viable.
Doing the same for Pets is a whole different story:
Getting all the max size and especially gold/ rainbow variants of all the mythical Pets and especially for divine or even Celestial Pets that may be released eventually is just not possible: The money required goes way into Trillions even with all the boost abilities that are available and that is not even the difficult part: Actually buying all these eggs is even more limiting.
So maybe there should be other goals for the Pet section of the Journal, like finding all the different abilities?