Photos are not actually stored inside of Lightroom, and so you can indeed import RAWs and JPGs into Lightroom and use up only slightly more disk space. No it does not take 4 times the space; the photos can be on an external drive, and not on your laptop's internal drive, and they become available for editing whenever the external drive is plugged in. Furthermore, you could use smart previews to allow editing of the photos even when the external hard drive is unplugged.
But if you're going to always assume that Lightroom works the same as Aperture, you will have a very long and frustrating climb up the Lightroom learning curve. Better you should start from scratch and learn the most efficient ways to use Lightroom.