Here's how I would approach it: train a dreambooth model on watercolor style images, then run image-to-image using that model.
For examples of what dreambooth models can do see: https://synapticpaint.com/dreambooth/info/ (sample images here generated using a "modern disney" style model).
If you need help getting this set up feel free to email me! This stuff is probably not harder than getting gimp to run in a container.