I built a pretty big station the first time. Later on I decided to start making them a lot smaller and simpler just because of framerate issues. This is one of my recent ones, able to stock a decent amount of fuel and dock quite a lot of ships at once. The only lights on it are illuminating the docking wings. What a station needs depends on what you're going to use it for. I'd imagine most KSP stations are used for refueling, in which case all you really need is a command pod (piloted or AI), a fuel tank or two, docking ports and maybe a couple of solar panels + batteries. Your only power drain will probably be lights, and those large solar panels generate so much juice, large arrays are mostly cosmetic.