6 months PRE- tummy tuck

I can't answer all your questions but know that Drs usually have guidelines they give patients that state how much you should weigh and how long you need to sustain that weight before they will do surgery. But there's many Drs with various standards so my advice is to lose as much as you can healthily lose until your surgery day as it will give you the best result. When I was nursing I kept my supply up eating around 1700-1800 cal and burning around 1000 cal a day exersizing so it really depends. That's just my experience though. I'm interested in a tummy tuck (same stats and with 3 c sections plus a couple more surgeries there!) if I get to about 165 or 170. So let me know how it goes!

Set your goals here for 0.5 - 1 lb per week loss (base activity level on your job) and eat maybe 50-75% of your exercise calories back.
When in the gym I suggest adding strength training (stronglifts 5x5 is a free beginners lifting program or some good books are New Rules of Lifting for Women or Strong Curves). I suspect that you will actually notice a huge change in your abdomen as you lose weight (I know I have and I've had 2 c-sections).
Lots of changes, but it took awhile (mainly because I was pregnant at the end of 2013 and beginning of 2014):