Clustered indexes specify the physical storage order of table data (this is why each table can only have one clustered index). The insert operation will usually be faster if there is no clustered ...

Non-clustered indexes can be numerous in SQL Server 2008 I remember from my Sybase days that SQL Server tables could support up to 255 indexes. One clustered index and 254 non-clustered indexes.

Non-clustered Columnstore Indexes are also getting some enhancements in SQL Server 2016. The most notable of these enhancements is the ability to be updated.