Specifically the number after Caramel Malts, 20L, 60L, 120L... Does this refer to the Lovibond rating for that malt? If so, will a 1lb of 120L provide 2X the color of 1 lb of 60L?
Yes, it is the Lovibond rating. In your example, the 120L would ROUGHLY provide 2x the color if everything else was just base grain, but it wouldn't be exact.
The color will be different yes, but the flavors are also very different. Think of it this way, the barley has been malted for longer periods of time to increase the lovibond rating. On the lighter end of the scale (20L) you will get a much sweeter, candy like flavor from your malt; when you get into the longer roasts (120L) you will get richer, roastier flavors from your malt.