I do not believe anything has changed.
You can start with the most important images:
1) vnsprite.
2) 3 or 4 profile images with different closing (bikini, magic robes, casual).
3) battle sprite
4) resting
5) straight sex (vaginal and anal)
6) gay sex (lesbian)
7) blowjob

portraits with base emotions (one each if possible)
9) Combat image (different from battle sprite which is a smaller image to be used in BE, this one is used in training)
10) Nude (at least one nude image without sexual content)
11) Jobs images: Maid, Stripper, Prostitute (provocative), Warrior (combat image can be used here), Waitress, Manager (formal clothing I guess, can be a profile type image).
I this this will make a working pack, rest can be added later.
Maybe it would make sense to make all the image with transparent or simple background. Such a pack may look really good in the game.