Assuming that you are talking about a soil nail wall with an MSE wall in front of the soil nailing, the FHWA is very soon to publish a design manual on the subject. The basic sizing parameters are that the MSE wall should have L > 0.3H with the top two layers L >0.7H to prevent a tension crack. The internal stability of the MSE is analysed conventionally for rupture and pullout.
I undertand your concerns about global stability. Check out Talren V4. It allows you to model the whole section simultaneously including different reinforcement types such as anchors, nails, grids, strips; construction stages, and load and resistance factors in the same model. Alternatively you could always use any of a number of FEM or FD packages.
Hope this helps.