Definitively love the look you gave to megaman. He's cute, readable and even show some determination once his helmet is on. Regarding the NES restriction, they have been über-detailed in this post, but to summarize them, you can have only 3 color + transparent for both tiles and sprites, plus a backdrop color (that shows through transparent pixels of the BG tiles). You can have different palettes for different tiles, and you can change the backdrop color while retracing the screen (though i wouldn't bet on more than 3 or 4 changes per screen).
You also have a single background layer, so what you sketched in your level will either be weird for the player (e.g. scrolling a deep-perspective picture without altering the perspective lines) or a terrific challenge to the programmer (reprogram those building side' tiles so that they actually give depth-field feeling. In the case it's just a static screen, i note that far buildings have orthogonal perspective when the front containers have regular perspective, which is ... odd.
