What are my odds of getting into Stanford if I have a good overall GPA of 4.29 and I am Mexican-American and I come from a poor family of 10 and I have about 400 hrs of community service?

as of 2010 Stanford's acceptance rate was 7.3% which is obviously low. The largest deciding factor for acceptance is your application essay. The gpa and minority status help but the essay is what can put you over the top. Even if you do well on the essay, you stil have the 7.3% to deal with. Best of luck!