How about Imogen? I don't think Sophia quite fits. I think Imogen is very pretty and feminine in it's nickname form - Immy - and very grown up, mature, strong and adult as is... Is it an option?

As for Nate Spencer - Is it Nate or Nathaniel, peresonally I think Nathaniel is better and Nate as the nick / more commonly known as name.

Otherwise I think it all sounds fantastic.