I'd suggest using Fitbit, properly adjusted if required, for it's infinite levels, rather than you guessing from 5 rough levels.

If you do weights, log it on Fitbit. Almost everything else is probably good to go unless you are using step-only-based device - in which case several workouts should be manually entered (swimming, elliptical, stairs, spin/bike, ect).

That way as seasons and activity level change - and they do - you've got a running 2-3 wk average of weekly TDEE, and you can set your eating goal based on that infinite level average.

But no - once you manually set a number on MFP as your eating goal - you must unsync Fitbit, because that adjustment is from MFP correcting it's estimate of daily burn with no exercise to match Fitbit.
So your eating goal and MFP's daily burn estimate are starting from different foundations to just add on Fitbit adjustment.

I keep my Fitbit synced because I like to see the exercise figures. I know what my target is and I work to that rather than the "what's left" number. However I don't log any extra exercise on the Fitbit app - I have one with heart rate so if that's elevated through lifting it will show as extra Cal's burned. I also like to know if I'm having a particularly bad day, or if something unexpected happens (a spur of the moment meal out for instance) I have some spare cals to use.