I can tell you right now that my own personal strengths lie in coding before the visual 'arts'. Though I have dabbled in 3D and really want to learn more about creating models, etc...Coding might be easier for me to grasp. (That isn't going to stop me from trying though...I got a copy of Maya the other day and I'm going to begin toying with it when I get some free time). I do a lot now with web programming, and I think with some examples and templates and the scripts from the original game, I should be able to pick up scripting for this easily. Hopefully some kind of 'reference guide' will be posted for functions that are already implemented, etc....
I have high hopes for being able to easily create my own stories and scenes...as I writer (I RP extensively and sometimes write on my own), being able to visualize some of these stories, even if they are cliche, will be beyond amazing!
On the subject of 3D models, First, I'm going to begin by trying to make some simple toys and things...someone suggested the ability to do fisting in another thread and that gave me an idea

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Second, I'm really hoping for the ability to somehow 'copy'/convert them from other mediums...for instance (this is just an example), if someone were to take a modded body file from Klub17 and convert it to this game....should technically be possible since the bodies have functioning pussies/anuses....might be as simple as re-rigging in maya to the skeleton supported by XSP....but then I might also be FAR off track....
And Last...maybe this doesn't even belong in this thread...but since we're talking about modding...I wonder how hard it would be to convert some of the 'bottles' that are in game to be used for...ahem...other uses....and what about those energy drink cans in the gym?.... AND WHERE THE HELL IS THE FOOD IN THE GAME? The apartment doesn't even have a kitchen!