Went to the Auckland Art Gallery earlier the week and met up with @bgrtworks and talked art and painting rooms using a stylus and iPad. Also the imperfections in great art that make it what it is.
Below - First 30 min screen shot - basic colour
70 min mark main details / shapes
2 hour mark fix the perspective
just over 3 hour mark - Final fun details
Size for printing / sharing
4 hour photo study