Weight loss math help: if BMR is 1700, only eat 1700 cals a day?

If you plugged your stats into MFP and it told you that you could lose 1 pound (per week) eating 1500 calories (plus eating back exercise calories), then try that for a few weeks and see how it goes. If you are losing too fast, bump up the calories a bit. If you are losing too slowly, drop them a bit.

If you do not eat your exercise calories back, you may find yourself running out of energy and unconsciously reducing your non-exercise activity to compensate. On the other hand, many exercise calculators and machines give wildly inflated exercise calorie counts, so it's a matter of trial and error there. I usually eat 50% of mine back unless I am really hungry, in which case I eat more of them back. Lower intensity exercise does not seem to jack my appetite up as much as high intensity exercise, and I can go longer with fewer injuries so that is where I put most of my exercise time.

Dietary restrictions are a recipe for failure for me. I start off with grand intentions of a complete diet overhaul, but it never sticks and I feel crabby eating foods I hate. Small changes work better for me. If I can incorporate one new recipe in a week or an additional veggie serving in a day, it all helps over time. By trial and error, I've figured out how protein, fat, and carbs (also fiber and water) affect my sense of well-being and feelings of fullness. If all of a sudden I start feeling hungry at night, I know I need to save a couple hundred calories for a snack then, even if I normally don't snack.

Don't bog down in the details right away though. Just start somewhere, don't eat too little or exercise too much, and adjust from there.