Here's my workflow in case you are interested. After sketching the images and storyboard (see storyboard below) I then created the final illustrations with my iPad Pro/Pencil with the Tayasui Sketches pro app. This app is great for creating and exporting raster artwork. So. Much. Fun! The watercolor features are truly astounding. I vectorized the finished art in Adobe Illustrator then imported them into my UI design layout in Sketch and animated the mockup with Principle for Mac, voila!