How many calories?

I know this has possibly been discussed a lot, but I'm a bit confused about how many calories to eat.

In the 80-10-10 book he describes the easy way to work out required calories for BMR is to times weight by 10, but he says either current or desired and that's what confuses me. I'm currently 182lb and would like to get back down to around 135lb. So I want to lose about 50lbs. I have read all about the starvation study conducted in the 1940s, so know that calorie restriction diet is not the way to go. But do I go by the weight I am or the weight I want to be??

I also notice that a lot of the people on here who have successfully lost weight, do a lot of daily exercise. I'm not able/ willing to do that much. I've started back into my exercise which currently is doing 20minutes of cardio (elliptical trainer usually) and then a weights session which is probably another 15minutes plus stretching. I plan to increase this a bit as I get fitter, but I have a young child who needs my time (and restricts how much sleep I can get) and I work etc, I'm not going to be running 10km/day like some of the people here. So I'm wondering about people who have successfully lost weight with just moderate daily exercise not lots..?