There are three ways that you can “import“ Images until Lightroom. You can add them where they currently exist on your computer and not change the file structure, you can copy them from a card to another place on your computer, organized by chronology or arbitrary folder structure, and move, where you can move your images from one part of your computer to another. So no, you’re not locked into any proprietary folder structure. I teach Lightroom, and my recommendation would be to have the program download your images by year and month and then put your better images into collections which are virtual places found only in the catalog. images into Lightroom. You can add them with a currently exist in your computer and not change the file structure, you can copy them from a card to another place on your computer, organize bye chronology or arbitrary folder structure, and move, were you can move your images from one part of your computer to another. So no, you’re not locked into any proprietary folder structure. I teach Lightroom, and my recommendation would be to have the program download your images bye year and month and then put your better stuff into collections which are virtual places found only in the catalog An image can be in multiple collections. One thing you may notice after a while is that the folder structure is only visible in the library module, so Lightroom really want you to put your better work into collections where they are accessed in any module.
Of course I would love to work with you and help you migrate from aperture if that’s what you’ve used, or set up lightroom to get you off to a good start. I’ve helped hundreds of people over the years teaching at colleges and universities and through Wyzant. Please contact me if you’d like to work together