You should consider looking at the latest PPM update if you are comfortable with Fusion. It may make the whole thing far easier for you to get started with.
If you are using PPM with OpenSCAD, you need to write the text as an object. Everything is code in OpenSCAD.
You can add an option in PPM with OpenSCAD to give users the ability to upload an STL that THEY have, which you position in code.
It is based on this, with changes.
If you are not comfortable sharing your model source, mark the upload as closed source.