The 12V LED strips actually start to light around 8 volts, there are three LEDs in series with the resistor.
You would want the LM317T for the lights if you want to vary the intensity. You can use it in either a variable voltage mode or a variable current mode. I like the variable current mode, that's what I use for my lighting modules. Here's a diagram of what's in my lighting module, you can wire this from components if you choose. If you KNOW you'll never run DCS, you can omit the choke. This circuit gives you about 5ma to 45ma of current. I find at 45MA of current, the LED strips in an 18" passenger car are way too bright for my tastes, so this works out pretty well.
