The EU is just a political union. It can break apart without necessarily destroying the economies of its member states.
Wrong. What can be sold in what condition is regulated by law. Countries have different preferences of what is allowed and what not. This law requires the governments to sit together, argue and come up with regulations. The single rule for all they decided upon is what makes the single market.
The UK has to at least implement everything the EU decides. Without a say in its proces. Big win.
Im sorry to tell you that you are overly optimistic. Trade deals are a very hairy topic. Look at TTIP, it will likely fail.
You know that the Norwegians pay for access to the common market?