As much as it is possible to use special functions to set user security, it is very complicated and prone to user mistakes procedure.
Can I suggest something?
Why won’t You create Your security rules based on Windows Groups and in the end, when You will add user using script just use special function to add that user to specific windows group so he will automatically inherit all security settings from that group? In that case it is unnecessary to setup every user independently.
Let me know if that is sufficient. If not, can You explain more why You cannot use groups and then just assign to that groups users and would like to use seperate user security instead?