If I were you, I would set the amount of stars in FRED to zero and use a skybox instead, but that's because I think the retail stars suck, not to mention the bug where they are rendered differently in relation to other background elements, which causes the stars (and suns and subspace node visualizations) to move in relation to background when you're turning your ship...
As to finding good images of solar system... dunno, perhaps Celestia Motherlode would be good place to seek, at least they have high-res textures. Dunno how much renders they have, and whether or not they are given to "public use" or not.
Anyway, if you want to use really big planets, don't use the FRED's stretching system, instead use skyboxes. They result in less distortion IIRC.