What type of mortar should I use?
The mortar should be matched to the brick hardness (or stone hardness).

A soft, reclaimd brick might be matched to a Type N (750 PSI)

The type S, at 1800PSI would be my guess for these bricks.

The M, at 2500 PSI would probably be too hard.

A great tutorial from the Nation Park service:

Repointing Mortar Joints in 
Historic Masonry Buildings