It's possible to paginate these APIs. We know one mylist/series can have up to 500 videos, and it's possible to have 25000 videos registered across all mylists, but I'm not sure if there's a limit to a number of lists: https://qa.nicovideo.jp/faq/show/557
It's possible to paginate these APIs. We know one mylist/series can have up to 500 videos, and it's possible to have 25000 videos registered across all mylists, but I'm not sure if there's a limit to a number of lists: https://qa.nicovideo.jp/faq/show/557