Personally ( not a recommended solution for everyone ) I would not use the Railing tool to model that IF
it needs to be in a comprehensive and detailed Interactive Schedule showing every nut, screw, washer, bracket, plate, tube, post cap, etc.... when that is the case, I model every part needed in an Interactive Schedule as individual parts. Place the post assemblies of parts (group), model the panels as walls.
The main reason I don't use the Railing Tool is because it takes so long to configure all the settings to get what you need, you could have must modeled it with other elements that are much easier to Schedule. And in the end, you will have what you really need instead of almost what you need. I am not a fan of the Stair or Railing Tools for that reason. However, there are still many other good reasons to use these tools and you can ( with a lot of effort) configure the Tool to do what you a
As with everything in ArchiCAD, how you model it depends on what you need to do with it.
Most Railing systems are an assembly of manufactured components. Many times you can get the CAD parts or drawings from the manufactures web site. Convert them to .gsm parts and you can get them into an Interactive Schedule very easily.