Vertica needs 40% free space ?

1. Not mandatory, recommended.
   Keeping a certain percentage of the file-system free will help to to prevent filling the disk to the point that the system is unusable. Also, the anti-fragmentation strategies used by Linux file-systems require that the disk is not close to full.
   Free space ensures DB growth, load files area and in addition Vertica use TEMP area to store DML-generated temporary data there.
2. Technically it is possible but from performance perspective it is not recommended to share a node with other demanding activities.

Thank you for the confirmation.