Max number of fœtus is 3. I tried to go over, but then the game doesn't allow you to save, and you only give birth to one baby.
Tweaking the number with CE allows you to always give birth to triplets though. I'm just not good enough to get pointers...
The max retainable breast size is 104. You will be able to go over during prenancy, but after birth you'll get back to the maximum, 104.
The game already implements a system to change tan colors. Cannot be to hard to add a new textures. Same for the Hair.
A mod to get bigger nipples as the preganany and the breastsize increase would be great.