I'm not sure I agree with you. Spending time immersed in a language is the best way to learn the language and learn a new culture. I've been to Miami you don't have to speak Spanish because you will find someone who speaks English at some point. what do you mean by "sock..."? Miami is still the U.S. in my opinion - nothing wrong with just not the same thing.
I Think it s a fantastic idea (i have done it myself for English young, then Spanish in college). However, I think you may have to pick one or the other. Baseball or Spanish. The logical thing would be to start with Spanish. In that case, I am not sure I would pick DR honestly.
Then, once your son is better in Spanish and more of a traveler, you could refocus on the baseball.
Just my 2 cents.