Actually, it is best to keep your fat below 15-20g if you can, though for most people it is nearly impossible. You also need to try to get lots of protein and make sure you have your necessary vitamins and minerals before working on cutting calories back too far. The general healthy diet ranges from 1200-2000 calories, depending on your activity level and lifestyle. This came personally from a doctor to my mother.
With popcorn, really if you buy the kind that is unsalted and not buttered it is perfectly fine. Kettle corn is fine as well. You just have to watch what kind you are buying. Some of it has as little as 0-5g fat per serving and only 10-35 calories. (I checked my kitchen, we have a few different kinds lying around XD ).
I just checked a popcorn box and there is about 13g of fat in salted and buttered popcorn. It says that the kernels themselves have about 110g of fat per serving but after it is popped there are only 20g of fat per serving.