My plan, questions & tips needed.

I'm going to be stuck at school while my boyfriend takes his classes so I want to make the most out of it. There's a small fitness center at the college with treadmills, step machine & some weight lifting stuff. (Bench, some thing you move with your arms & something else)

I am a 25 year old female.
I'm 5'6" & weigh between 148 & 154 lbs depending on the day. I wear a size 7 in juniors in jeans. My doctor told me I needed to lose 15 lbs.
Here are my measurements:
Arms - 11 inches
Waist (Below rib cage) - 30 inches
Stomach (Below belly button, biggest part of stomach) - 37 & a 1/2 inches
Hips (Largest area with butt) - 41 inches
Thighs - 24 inches

1. My goal is to be 120 - 125 lbs by Halloween. So that means I need to lose 25 to 30 lbs in 72 days. Is this healthy & possible?

2. I'll be there 2 to 4 days a week about 2 hours at a time. I was thinking of eating 1200 - 1500 calories a day.

3. I was thinking of doing the treadmill & stair climber an hour a day & some type of weights 45 minutes or so. On days that I don't go to the gym, I will try to walk at least 30 minutes. Does this sound about right?

4. My arms are really flabby, how long before they tone up some? My hip bones are large. If I lose weight, will I lose a pant size even though my hips are bigger?

5. What's a good app to use to keep up with my progress? I'd like one that keeps up with my weight/measurements, exercise, calorie intake & calories burned.