Suggestions for a Spanish/English site

I am designing/coding a wordpress site that needs to be available for Spanish speaking and English speaking visitors.
Does anyone have any suggestions for the best way to go about this?

The plan so far is to either have two different headers, with different menus to two sets of each page, in Spanish or English.

Alternatively, we could have a “splash” page that directs to either language, although that will affect the seo of the site.

Any other suggestions welcome.

Thanks!