What is a good thickness/ratio of concrete to stones/these are small
stones mostly/ do I need to reinforce with iron
Reinforcement design depends on height and load resistance.
Rather than full slipform design--see Flagg/Nearing/Kern--I prefer
using a plywood form at the back and none at the front, so you can see
how the face stones appear. You will be looking at them for a very
long time, hopefully.
What I have evolved to is a stone foundation topped at ground level
with a reinforced footing that includes a mower lip. Near the back of
the footing have rebar sticking up, into what will become an area of
more concrete and smaller stones fitted around the rebar, backing the
biggest, prettiest stones for the front facing.