Can I set, on my own stock system, the max margin limit or avoid the buy on margin feature so that leverage is not alowed and buying power = nav-invested assets ?


No, we automatically apply 50% margin on all stock trades (for stocks over $5). If you do not want to see the effect of available leverage, simply treat your C2 Model Account as if you have 1/2 the buying power that C2 says you do.