Playlist off line and quality

[Steven66]

On my android device I frequently use the off-line feature to listen to playlists I downloaded previously via wifi. Unfortunately the size of the downloads is limited. I have some questions related to this:

1. Is the size of the download limited by the total length or by the size of the files?

2. I currently use the normal quality to play off line and extreme quality on-line. If a track is downloaded and played back while I am online which quality do I hear: the downloaded file in normal quality of a fresh stream of extreme quality?

3. Some of my playlist (I frequently use playlists of other users) are too big to download completely. I than receive an annoying message the download cant be completed. Can I avoid this?

4. Is it possible to select a part of a playlist for downloading or can I select a part of a playlist and copy this to a new playlist?