I am new here and about to take the jump from point and shoot to SLR. I will be using photoshop to edit most of my pics. Most of my photos will be 4x6, some will be 8x10 and a very small few will be larger sizes like 16x20 or even 20x30. What specs should I look for in a SLR in order to be able to edit and crop pics of the sizes I have listed (mega pixel, ect)? Thanks