I want to try creating new portraits for all the characters in my own style, but I don't know where to find the place holders. I don't know the dimensions, either. Is there a tutorial somewhere that can get me started, or maybe someone can lend me a hand? Heres my DA, (http://avannteth.deviantart.com/) so you can get an idea of my skill level for art. Modding, however, I'm clueless.
First off, awesome work! Excited to see what you do with your portraits. In the tools section of this forum you can find .xnb extract along with instructions. In the content folder of Stardew you'll find "Portaits". Extract them to find a .png file.
Here are all the base game portraits. You'd just want to make sure yours fit in the same dimensions and have the same sort of expressions for each spot (like if the 2nd row down has a blushing picture, then make sure yours shows someone blushing too).