In Most of Miami-Dade (except for the Northeast, Miami Lakes Miami Beach) the default language in which you will be most likely first addressed will be Spanish.
Hello Jamz : You will need to check out WikiPedia.com to find out which areas in Miami use Spanish or English. As for the 1st part of your question, Spanish is used in Miami every time someone speaks it !
more spanish than english, spanish about 90% of the timeall schools near me have a ratio of 81% hispanic, 9% black 1% asian and 9% whites(i searched online)
99.999999999999999%