With a Paint by Number kit, or coloring Book Taped to the Opposite Side. Usually this entails Acrylic Paints but if you install an interior pane of Plexiglas, Clear Plastic or even Removable Transparent Film you can paint the Reverse on the backside to use less expensive paints for a Similar effect
Sandy....or sand well, clean then paint
I'm Linda. I've painted a lot of windows in my lifetime. They are really not that hard as long as you tape off the glass, make sure the surface is clean and free from dust and tape along the walls so you don't get paint where you don't want it. Here's a tutorial that shows what I do to paint a window. I hope this helps. Wishing you the best.