When I ran the code it threw an error on this line win.radiobutton0.value = true;
Object is undefined. This is because the way you have the dialog structured the button is part of the info
group within the window. The line should read
win.info.radiobutton0.value = true;
This should toggle radiobutton0 on initially.
You don't have to use a resource string to craft the dialogs if you don't want. Individual elements can be added by creating a reference to the window object (or to a pallate or panel) and using .add()
For example:
var w = new Window ("dialog");
w.alignChildren = "left";
var radio1 = w.add ("radiobutton", undefined, "Radio Button 1");
var radio2 = w.add ("radiobutton", undefined, "Radio Button 2");
radio1.value = true;
w.show ();
This is the most thorough reference on ScriptUI that I've found.