The name of the barrel doesn't matter, just link it to the turret base object. And there's no way to specify object rotation axis right now, but any User Properties you set on MAX will be translated to subobject properties in the POF.
And Sandwich, yeah, that could define the radius, but I don't really like the way you'd set a path then. Right now it generates the radius automatically, you can adjust it in PCS or other editor. I'll think about the light thing.