I've mostly answered this stuff in the other comment, but I'll go through a few things here too.
1. You're right, Regigigas is organic and her being a Sub-Legend means she won't have anything specific based around her, I will be bringing her back later on for one specific thing in Chapter 7, but that's a secret!
2. Yep, I am going to keeping up the gimmick, a new one for each Chapter, thankfully the comment above gave me a good idea for what to do at the end of Chapter 4!
3. Jenny and Joy are staying as a MAYBE for now
4. Giving the girls a good rub down when they're at their biggest, that's going to be the new gimmick!
5. What you wrote is more or less my answer.
6. Finished the breed & capture scenes, just staring work on Marley, I'll write their repeatable sex scenes at the same time to avoid burn-out