I Need a Hip Replacement. Should I Do It Before I Have My Tummy Tuck?

You should do what needs to be done before what you want to be done. I know, it seems seductive to consider that losing some abdominal weight via tummy tuck will "make it easier" on you replaced hip, but you really won't lose that much additional weight with the tummy tuck, and once you have your ailing hip replaced, you will be better able to recover properly after tummy tuck. If you decide to do tummy tuck first, then your hip make make early ambulation and activity more painful, increasing your risks of deep venous thrombosis (blood clots), pulmonary embolus, or even death. Though these risks are small, why take any chance when they are avoidable?

It seems to me that you are on the right track toward loosing weight and trying to improve your shape.  You now have a joint problem that need to be addressed. It necessary that you deal with the hip problem first.  this would definitly improve you mobility and possibly loosing more weight and after tummy tuck were you need to mobilize early after surgery. 

I would definitely recommend getting your hip replacement first. Yo may lose more weight after being more mobile; this will give you a better result for your tummy tuck.   Also, you will be able to get up and move around better after your tummy tuck; this will speed your recovery and decrease the change of a blood clots.