Hey DS--If you're counting calories, then let me put in a pitch for the book "Calorie Queens" (there are separate threads online). The reason I mention it is because it addresses your concern about how much food you can eat once you hit goal weight. CQ uses a rough guesstimate of 12 calories per pound to maintain a particular weight. There are calculators that work out to about this amount too (partly dependent on whether you are completely sedentary during the day or whether you get up and do some moving around). If you assume that at goal weight, you'll be a bit of a bouncy, happy person, then 135 x 12 = 1620 calories to maintain that weight. CQ advocates BEGINNING a diet by eating your maintenance calories. Some people may then find that they are aiming for a goal weight that is too low--that they are just completely unhappy with that number of calories and may then want to re-evaluate whether their goal weight is realistic for them. Others may be perfectly happy. So....CQ would say you should just eat about 1620 calories now and your weight loss will be initially pretty quick and then slow as you approach goal, but what you're doing is not really "dieting" in the traditional sense, you are establishing--right now--the eating pattern that you will need for the rest of your life.
All that said, I tend to agree with funniegrrl that 1500 (or 1600) might be too low at your current weight. So...let's just assume that we're talking 300 pounds (a round number for math which I suck at :LOL

: 300 x 12 = 3600 calories to MAINTAIN that weight. If you eat 1500 calories a day and do NO intentional exercise, that gives you a daily deficit of 3600-1500 = 2100 calories. Thus, for a week, your total cal deficit is 2100 x 7 = 14,700. It takes 3500 calories to lose a pound, so 14,700/3500 = 4.2 pounds lost. Hmmm. That might be a bit steep initially and with such a big deficit every day, your body may SLOW metabolically (think it's starving) and that is really the opposite of what you want to happen. A seeming contradiction in this activity is that you have to EAT to LOSE weight. You can play with the numbers from here, but I think that maybe setting your intake to allow for a 2-3 pound loss for a while might be a healthier weight loss range? (others can chime in). For a 300 pounds person to lose 3 pounds per week, that's a weekly deficit of 10,500 calories, thus a deficit of 1500 cals per day, thus a calorie INTAKE per day of about 2100. For a 300 pound person to lose 2 pounds per week, that's a weekly deficit of 7000 cals, thus a deficit of 1000 cals per day, thus a calorie INTAKE per day of about 2600.
Caveat: none of the calculations above takes into account intentional exercise. You may find that if you begin exercising regularly/heavily that you will want to INCREASE the calories in to maintain a healthy balance. (just kinda depends on how much you eat to start with, how much you exercise, and perhaps most important, how you FEEL).
ANYWAY....as far as fat grams versus calories, I personally find that I cut down on fat just to get more FOOD in my mouth to fill up :-) But...I *do* have some fats everyday (I really don't want my hair to fall out or my skin to get any drier than it is!). If you're having trouble getting your calories in (I always find it weird to hear so many people say that!), peanut butter is an oft-cited recommendation or nuts in general--good fats, high calories, very low volume.