50 pounds by your birthday is reasonable! I'm currently on Weight Watchers and I exercise 4 to 5 times a week. 3 days ill go to the gym and do 35 mins on the elliptical and strength training and the other two days ill go on long walks with my mother either 3 or 4 miles, but i enjoy it so much. I usually lose 2 pounds a week which is considered healthy weight loss. I think you should do 3 days of 35 minutes exercise like myself and maybe one day of an hour exercise...because doing 1 hour of exercise everyday or whatever you'll get so bored and want to quit. take it slow at first.
as for your eating, i would encourage you to look at fitness and health magazines they usually have menu plans for calorie counters like yourself and yummy recipes!