Nothing I can think of. You've already got several Apple products linked to the same Apple ID, you're adding one more. You can, when setting up the new Macbook, use a backup from the other Macbook (using Time Machine) to set up the new one. It will basically produce a clone of the other Macbook with all the same software, settings and documents on it. Depends on whether you want that of course, and you will have to check whether all the software allows this. A Microsoft Office installation might protest at being used on two systems at the same time for example.