Do not worry about the water pump. In the manual is not written that the pump should be changed, at least this is written in mine, just to be checked for leaking. Changing it, is true, is a common use and I do it also. The last one I have changed it was in a very good condition. But I had already ordered a new one so I replaced it.
The engine is bullet proof. New oil and filters at proper time. The only major problems come with the EGR in my opinion. At some point stops to work properly and from there some other problems. You can clean it, replace it or disable it. As you want.
My engine has 120k km (I am from the continent, I count in km, sorry : )) ) and no problem, except the EGR. I think I will replace it.
Anyway, GT is a nice car, good looking and great sits. You did there a good deal.
Do not be afraid to give some revs. Although is a diesel it feels better at high revs.