How should they fit?

Wannabel. If you are a male the heel should be a Cuban Heel. The shoes are very flexible that the top dancers use. That means the toe part can be bent to the other end of the shoe whilst holding them in your hand. Don't want any surplus at the toe. They should fit like a glove. The weight in Latin is towards the balls of the feet. The Cuban Heel takes care of that without trying. If you want to be a Latin Dancer get 2003 World Super Stars Dance Festival LATIN. In the Rumba see what part of the rear toe is in contact with the floor on a Rumba Walk, Man or Lady. You will find the the toe is completaly turned under and what would be the top of the toe nail is turned under onto the floor. Hence the flexible shoe.

if you're a female, you need at least 2.5", or even better, 3" heels that fit tightly. In latin dancing the ends of your toes should be in contact with the floor. This will require you to buy a smaller size; In reality I am a nine but in latin shoes I wear a 7.5.

If you are a beginner, however, you might want to start with a lower heel. Depends on how good your balance is and how strong you feet are to begin with. Your teacher should be able to give you some advice about this.