Which design pattern to choose in Golang

I understand this question seems obscure. Though I really am scratching my head around this.

I have a tremendously big XML to Marshal. The XML might go upto 1900-2000 lines at its peak level with around 21 levels of nested tags (~ 600-700 different types of XML elements to fill).

Currently I am preparing data model in Go from which I would be able to do xml.Marshal(). However, I also need to do lots of validation checks over this 600-700 fields before marshalling. They also have inter-dependency over each-other.

So, What should be the best design pattern I should choose to develop the solution?