First, I am by no means an expert. However, my husband and I have recently entered into a gym membership and both of us are classified as morbidly obese. He started at 6', 300 lbs and I am 5'3" starting weight of 226 lbs. In the last 80ish days we've lost 48 lbs between us (19 him, 29 me). With that said, we have developed, researched and came up with a gym routine that works for steady, healthy weight loss.
Your post said you plan on doing 15 minutes elliptical and then 30+ minutes on the treadmill. First of all, I caution you on overdoing it, especially at first. When i first started, I could barely finish 15 minutes on the elliptical and 30+ minutes of treadmill equaled inability to walk the next day. So, I started with the low impact elliptical and utilized the stationary bike (which I would recommend due to strain on joints until some of the weight comes off). Also, 30-45 mintues of cardio total most days of the week (i.e. 5-6) was the recommendation I found and follow. I do split them however with weight lifting between.
That leads me to the most important part of your new gym routine. Weights are a must! To lose weight cardio is important, but muscles burn more calories than fat! A well balanced weight routine includes varied exercises with differing intensity schedules. For example, if Week 1 and 2 you do moderate weight with 10-12 reps for three sets, Week 3 and 4 you should increase the weight so the most you can do is three sets of 4-6. This makes muscle work harder, stretch further, and ultimately grow and aids in the weight loss. Also, mix up your routine every month so that the body doesn't get too accustomed.
Ultimately, our success has come from diet. I know I hate that word too, but here's the tricks we've figured out. Whey protein post workout (in the form of a shake) can be bought at nearly every chain store now fairly inexpensively. This feeds muscle growth and decreases hunger and the catabolic state of the body post workout. A post workout meal (1 1/2-2 hours) after is important and should include complex carbs and protein. You should be eating 200 grams of protein a day or more at your weight and size. On the days I lift, my afternoon snack is another shake or small protein. Include healthy fats, which decrease heart disease and satisfy you. I personally love my iceberg lettuce, tomato, cucumber and avacado salads (with chicken and italian dressing). You should probably be getting 50 grams of fat a day (but make sure it's healthy). The rest of your caloric needs comes from carbs. Now, complex carbs are the way to go of course, but you should take a "high carb" day every 10 days or so where you double your total number of carbs. This prevents your body from thinking it's starving and prompts it to give up the fat easier. Ultimately, you need to eat every 3 hours 5-6 times per day.
So, first firgure out your caloric needs daily. This is your weight in lbs x 14. Due to your size I would use a mid-point between where you are now and your goal weight. So we will use 200 lbs. as an example. 200x14=2800 calories/day. Protein is 4 calories per gram, carbs are 4 and fats are 9 cals. So if you are to eat 200 grams of protein (200 goal weight x 1 = 200 grams x 4 cal each = 800 calories of your daily intake should be from protein alone!) Fats are 50 grams (200 x .25= 50 grams x 9 cal = 450 calories from fat. Take 450+800 = 1250. So, if
you can have 2800 calories per day take 2800-1250= 1550 calories left. Divide the remaing calories by 4 (1550/4=387 ish grams of carbs) which gives you the total number of carbs you should max intake per day. That may seem like a lot of calories at first, but I bet you won't be hungry if you hit your protein and fat needs with a healthy mix of complex carbs daily. Cutting your calories too severly will leave you with no energy to work out, no building blocks to grow healthy muscle with, and make you prone to injury and longer recovery.
I hope this helps and good luck!