1. If you go to Display --> Heads up display you'll have several options you can check or uncheck for display, including poly count. Your machine sounds more than able to handle one jet and a couple of lights. Are you using a simple shader or are you viewing the whole thing with large textures (and with hardware-texturing on)? That could be stressing it.

2. You could use a point light with a glow to simulate a sun or moon. Just place it far off in the scene somewhere.