Answers

In Georgia a wall retaining over 48" grade requires an engineers stamp.

You might consider terracing and have two or more lower retaining walls. Be aware of hydrostatic pressure and provide adequate weepers to deminish concern for hydrostatic pressure. Good Luck!

You need to make sure that the material allows water to pass thru the block or stone.  Both choices can allow water thru if planned ahead.  Blocks can have weep holes that allow water to pass and many faux stone products are designed for drainage. 

Give a place for the water to go -

Mark, the answer depends on the topo ie the slope and terrain. Consult a local structual engineer..

proper drainage away, footers, rock, filter cloth, french drainect ect ( water is a hydrolic tool)

The design and layout are also important

*** A great engineer showed us the value of reenforcing a wall with a block planting box....  this gave an enormus amount of protection from failure

Best of Luck

Billy Gavigan

Gavigan