Calories

MFP does it for you. Input your information [height, weight, etc] into it, state how much you want to lose, roughly how much per week [2lbs/week is max, and is quite restrictive to most], and it tells you.

It's really trial and error. Mfp gives a rough guess but you'll need to try one amount of caloric intake and see what happens.

Trial and error is the best way. Calculators can be a good place to start, and will likely get you in the ballpark, but they make assumptions that may not be correct about you.

What I do and what I recommend to people is to eat at a calorie level that allows you to make good progress towards your goal. If you are trying to lose weight, eat so you drop 1-2 lbs/week. This assumes an average calorie burn from you getting in all of your workouts. This will be different for everyone, so you'll have to do some trial and error to figure it out. I'd start ~1600 cal/day. Hit this goal, along with your macros and getting in your workouts, for 2 weeks. If you lose 1-2 lbs/week, you're good to go. If you lose too much, increase your intake and repeat. If you don't lose enough, reduce your intake a bit and repeat. After a few cycles, you'll figure out what works for you in your situation.