Does this sound like a good diet plan?

635 calories a day is extremely unhealthy, and you will be putting yourself in danger if you eat such a small amount of calories. The average person of healthy weight consumes somewhere around 2000 calories. At most, I wouldn't go any lower than 1500 calories, and even then I might be a little worried. Even if your appetite is decreased, I would at least suggest eating 1500 calories a day.