Hi Roberto,
1) As of now line-breaks is not supported in labels. But for workaround you can look into labelMaxWidth.
2) Are you looking for indexLabel?
3) Using yValueFormatString you can format y values in both indexLabel or toolTip. If you like to format toolTip-content you can use toolTipContent in dataSeries level or by setting content in toolTip.
4) To start axisY from 0, you can set axisY.viewportMinimum to 0.
Here is an example.