Just a minor point about graphics. Make sure you determine the position of the sun and do your shading and highlighting consistently in all rooms. Assuming your images are all facing north, if your game is set in the morning, the highlights are on the right and the shading is on the left. In the afternoon, it's the other way around. (Sun rises in the east and sets in the west.) If you're in a cave, the shading and highlights depend on the position of your light source.
Of course not. I just thought I'd mention it for anyone that's using third-party graphics. It gives a feeling of professionalism that most users wouldn't even notice. If your graphics are reasonably symmetrical, all you do is flip the picture horizontally in your favourite graphics editor. Otherwise, you just switch the highlight and shadow colours. It's a little bit tedious, but very easy when using pixelated graphics.