Sma over nikah

Hi, I'm a Muslim man who wants to perform marriage with a Bengali woman. We are certain to perform SMA and get married. To retain our names identity, religion and lifestyle individually, respecting each other's way in one house. Only for a spectacle, we want to perform Nikah, to avoid any internal family issues. Post which we will be able to live freely on our choice and follow our respective religion and culture under one roof together. There is no force of conversion, change of name or practice we want to impose on each other. My question are as follows: 1. Does SMA supercedes Sharia Law? 2. In this case the Nikahnama is ineffective? 3. We both get to retain our identity name religion etc? 4. What complications can this lead to? 5. Does SMA and Nikah lead to any issues with buying property together? 6. Do we have to change any names on documents? 7. Are there are legal financial social issues we could face? 8. Does our child have to bear only one surname? (I believe it should be one, two surnames may cause issues to that child, is that true? What could be those issues? Please help.