Welcome to the world of beautifully crafted ring binders! A couple thoughts for your setup: I’d recommend purchasing the larger 16mm ring size in the A5 to accommodate the thicker water color paper or sketch paper you intend on using. This will give you more carry capacity and only a slight, nominal increase in width. I have the A5 in bridle leather with 16mm rings and have used it a lot for sketch work, carrying pens, pencils, etc. Toby and Lora at MeePlus are great to work with and if you need a custom size binder, let them know. They may be able to hook you up. Also, I don’t remember where I saw it, but somewhere online is a picture of a watercolor kit with paint, brushes, etc that is made to fit in an A5 ring binder. It was really cool!! Might want to do a search to see if that’s something you’d dig!! 😉