Challenge #4: Colors and perspectives don't even have to pretend to be realistic; they can be about inner psychology.
Henri Matisse, Woman with the Hat, oil on canvas, 1905, San Francisco Museum of Modern Art
Challenge #5: Things in the real world might be 3-dimensional, but a painting doesn't have to pretend to be; it can embrace its 2-dimensionality.
Georges Braque, Violin and Candlestick, oil on canvas, 1910, San Francisco Museum of Modern Art
Challenge #6: Art doesn't have to always be oil on canvas, for goodness sake; it can even be glued paper collage. (This art was part of the dada movement, famously also calling a urinal "art")
Hannah Höch, Cut with the Kitchen Knife Dada through the Last Weimar Beer Belly Cultural Epoch of Germany, Photomontage, 1919-1920, Neue Nationalgalerie Berlin
to be continued...