Playlists are saved on Yandex servers and are accessible to users from various computers. This means that you can, for example, create a musical mix at home and then listen to it and edit it on your work computer. Just make sure you're logging in with the same Yandex ID that you used to put the mix together.
Each playlist may contain up to 10,000 tracks or podcasts. There is no restriction on the number of playlists you can create.