If you're eating good food with low calorie density, it's definitely possible to eat a large quantity of food but stil not be consuming all that many calories- consider that for little more than a hundred calories, you can eat a whole bunch of brocolli or 4-5 cups of cooked cauliflower.
If you're doing a high intensity program like insanity, it's definitely important to keep your body fueled. Personally, I find my FS RDI to be a bit useless- it's pretty low if I enter sedentary for my activity level but it's too high if I put low active. Try using another calculator if you're not sure- I like the ones at freedieting.com. You also don't mention how you did with your RDI in your first week on FS- did you lose? gain? not track? Hard to know if you're eating too little or too much without that info.
Not sure what your question is for the exercise calculator. FS is configured to account for 24 hours a day (since you burn calories no matter what you do, it's just a matter of how many). It automatically starts you out with 8 hrs sleep, 16 hrs resting and any activities you add are taken out of your resting hours. If you have an HRM or other measure of calories burned, select "Other" and enter your cals manually. If don't have another way to measure it, I'd record your insanity workouts as circuit training (slightly lower) or calisthenics (slightly higher). Hope that helps!