how much should I eat?

This is a good guide as far as giving you an approximate idea of how many calories you should be eating. I would not recommend strict calorie counting as a way of life, however. Not only does it suck the life and fun right out of you, but its important to remember, the more active you are the more your body changes [more muscle, faster metabolism] and the types of foods you eat are going to effect you differently [i.e. processed foods vs fruits, veggies, & whole grains] so you can't go 100% off of calorie intake/output. cue calculator...

1] convert your weight in pounds to kilograms by dividing by 2.2
[your weight in pounds] / 2.2 = your weight in kilograms

2] multiply your weight in kilograms by [30 if you are a man] or [25 if you are a woman]
[your weight in kilograms] x 25 = amount of daily calories for a woman

 Now you can factor in exercise. Go here to calculate how many calories you burn.

source: Lippincott williams & wilkins Anatomy & Physiology 4th Ed