The authority of the Shulchan Aruch and the Rishonim.

Hello, Your Honor. How much, if any, are we obligated to the Shulchan Aruch and the other Rishonim in matters of halachic rulings? Do they have a binding status like the Gemara, less so, not at all? How is it expressed and what does it stem from if so? Is there a role in halachic definitions for a ‘halachic arbiter’ other than the Sanhedrin (I’m also asking about the period when there was a Sanhedrin)? In general, I would be happy to refer to columns or articles you have written to help me sort out the whole matter.