Question on best practice - keep empty partitions at both ends of your table?
Is it sufficient to ensure that there will be no data movement by ensuring that the new boundary corresponds to a future date or do I really need the empty partition ? 


If your partition function is RANGE RIGHT, then yes.  A partition split moves rows in the existing partition that belong in the new partition.  The new partition is the partition that contains the new boundary value.  So in RANGE RIGHT if the new boundary value is after all the rows in the table, no rows need be moved.

Hopefully you choose RANGE RIGHT to begin with so you don't have to have boundary values like 2015-12-31 11:59:59:999.

Depending on the indexes, the head partition may need to be scanned to discover that no rows need to be moved.