The US Bureau of Land Reclamation has a publication that can still be ordered, the title is something like "Moments and Reactions for Plates"  I have found this useful in modeling such conditions to take advantage of a more representative model.  The one-foot strip used in a cantilevered wall design would not account for the moment reversals created by the stiff counterforts...

In designing the counterforts you distribute the loads of a unit length of wall equal to the counterfort spacing. If you want to be precise take into account the moments due to the weight of the facing, the counterfort and the fill above the counterfort.  

Calculate the moments at intervals down the height of the wall to determine reinforcement required at various depths. The facing spannign between counterforts can be considered as the flange of a T-Beam providing sufficient fixity between counterfort and wall facing. The facing is designed for horizontal bending (usually iun upper middle and lower thirds to economise on reinforcement.

External stability for base sizing is designed as per standard CIP wall.

Hope this helps.