Hi there. 1.) DLC expansions are licensed to the account that you used to purchase them with. This does not pose a problem between Xbox One and Xbox Series generations. As long as you sign into your new Xbox Series X with the same account, you should be able to redownload the expansions you previously purchased from the Xbox store. Please note that the only expansions currently available are the Forsaken Pack, Shadowkeep, Beyond Light, 30th Anniversary Pack, and Witch Queen. Prior expansions are no longer available on any platform. 2.) You can buy the expansions without having a console and download them later by accessing the store from your console. Just make sure you sign into the online store and your new Xbox using the same account.