Writing, rendering and coding, yes.
Modelling: to some extent. Which is to say, it's just me, but modeling may be to big a word for what I'm doing. Daz3d comes with a few base models and a series of characters based off those models (hence the recurrence of several a-listers in so many games). In my case, I stay away from those characters for the most part, although I might use their skin textures for some variation. Instead I'm using several products that let me extensively morph and tweak the shape of the faces and bodies and finetune breasts etc., by pulling any of several hundred sliders. So a whole lot of customizing, but I'm not going into z-brush to actually 3d-model the characters, I'm not that skilled and too strapped for time.
I do mess about with textures a little, I might tweak skin tones on characters, or apply some deformities (I did in First Contact). I modify shaders and textures on outfits, and even 3d model the occasional prop from scratch if I can't find what I need, and I'll texture those as well, but all of it is relatively simple stuff.
But of course there's others involved, for instance I'll consult with my wife on outfits (which is to say, she'll drop by and demand to see what I came up with, then makes me change it if she doesn't like it), and come release time I've several people who've been kind enough to proofread my beta's for me, and in addition any top tier backer has access to the beta version and they'll provide proofing feedback on occasion too.
