There really is no way on earth to know just how much weight you will lose lose during any given time period.
The only thing that you can directly control, is what you eat and how much activity you do. The "better" you eat, and the more activity you do, the more likely you will get the results you are after - but not necessarily in 4 months time. But do know as long as you are creating a calorie deficit, the weight WILL come off, whether it takes 4 months, 5 months, 6 or longer. In 4 months time, if you stick to a healthy routine, you will be more then on your way to achieving your goals. And hopefully at that point you will be well "into" your new lifestyle and the healthy changes you make can be with your for a lifetime.
As far as what diets to recommend, well that is an individual thing. I mentioned above about a lifestyle change, because in my opinion, "diets", per se don't work. They have a beginning and an end. In order to lose weight,
and then keep it off forever we need to find something that we can keep on
continuing and DO forever. For me that's the combination of counting calories and eating very healthy, nutritious foods. I find what ever foods I eat, I crave. So in order to cease craving the high caloric foods, I basically elminated all the sugary, "bad" carb-y ones and ADDED in lots of low fat proteins, high fiber cereal, some fruits and tons and tons of vegetables. Now it's actually THOSE foods I crave - a truly miraculous, wonderful thing.
Take a look around the boards. There are many different plans. You need to find one that suits your needs. Something that you can stick with for the long haul.
Good luck to you. I greatly look forward to hearing more from you and all about your successes!!