I have managed to create a good looking vector model in Illustrator and I want to improve it by adding some textures. Will this make my model a raster image and no longer a vector?
In an Illustrator file you can have both vector shapes and raster images. Saving this artwork as AI will not transform your raster elements to vector. So any image/photo/texture included in an AI file stays raster, and this will not affect your model (artwork) which will be saved as vectors. In the end your AI file will contain both vector and raster objects.