Your first day of activation will be a mess. Don't even try to make sense of what the info tells you. At midnight the counter will reset and you'll be good to go on your second day.

I have my Fitbit synched to MFP. I look at Fitbit for steps, miles walked, sleep, etc., but I pay no attention to the calorie info. I use MFP for that instead. MFP takes the info from Fitbit and adjusts your caloric allotment accordingly. My MFP sedentary number is about the same, right around 1850 calories at maintenance. With negative calories enabled, I find it takes about 5000 steps to hit break even on days when I do other exercise. Break even seems to come up quicker on days when walking is my only exercise. Also, although I've never figured out exactly how it works, the more non-Fitbit exercise I do on any given day, the fewer calories Fitbit wants to credit me for miles walked. It works out in the end since Fitbit gives me too many calories per mile (around 100) on days when I have no other exercise.

Agree with above, don't try to take 2 different roads to the same destination, it will just confuse you.
Use Fitbit for exercise and step goals, ect.
Use MFP for food and the deficit side.

You can set Fitbit to whatever weight loss or none, the only thing it reports to MFP that deal with what you eat, is what you have burned so far that day.

Now - that can be affected by having the Fitbit Setting of Calorie Estimation enabled. Because then with no recent sync with your device, Fitbit will estimate what you burned up to that point, based on past days. If every day is about the same up until you sync, fine and dandy. If not, could be big variance.
And then MFP takes that figure and does it's own whole day estimate to base your eating goal on.

As to how many calories you need to burn to see positive adjustments - depends on how much of a weight loss goal you took. So you took 500 cal daily.

That means with 1850 eating goal without exercise, you'd have to burn 2350 on Fitbit to break even. Anything burned over that gives you more to eat.

In fact, that's a great way to set Fitbit fitness or burn goals, how much do you enjoy eating and can adhere to it, perhaps 2000, then add on the deficit, so 2500, and that's what you'd need to burn to eat at the level you'd enjoy and adhere to.

And steps can be very variable depending on weight, stride length, ect. So you'll find out what it translates to for steps.

And of course, if you do any non-step exercise, gotta manually log it, either MFP if syncing works nicely for you, or Fitbit directly if able to. Swimming would be obvious, but bike, lifting, elliptical, rowing, ect, all will be badly underestimated by Fitbit looking at steps.

Thanks for sharing about the calorie estimation feature. I actually had no idea what it meant, and I would rather it not estimate, so I can get a true real time read. I sync often, so it shouldn't be much of an issue, but you never know. I've been doing a lot of reading on this, and either I just can't understand, or there are too many mixed opinions. Are you supposed to log exercise that is not "step related" in fitbit or myfitnesspal? I tried it both ways, and sometimes I feel like I get a double read. I do yoga a few times a week. I would love to log a few extra calories, and map that I am exercising, so when I look at my chart, something is there. I get sad when it's all empty, even though I "know" I am exercising. Also sometimes I use the bike at the gym, or lift weights. What's your opinion on this? Thanks for the help!