Using tentacle dream as the example
Textures are located inside a story's scenes\textures and are in dds format
Fluids are located pack_tentacle_dreams\init\std\base Main_Base.dat
you can change a few things there like the colour and speed etc
Editing the characters is done in pack_tentacle_dreams\init\stories\tentacle_dreams\chars then the character you want and find their "Run.dat" and "Ref.dat"
Cant touch that yet is done with the characters init.dat under pose
ia_type = BODY_TOP_LEGS_ARMS_PRIVATE_SKIN_CLOTHALL;
so that the ability to touch all
as for adding new charater
http://wiki.xmoonproductions.org/index.php?title=Advanced_modding not too sure if this works completely yet i have not tried it myself
Hope this information helps