Had mine done two weeks ago.

Definately do the water pump, it's a £30 part and all the timing belt gubbins has to come off to change it anyway, so it's a no-brainer in my opinion. Same pump as 2.0 Zetec.

I used genuine Ford parts on mine as I know someone who gets me trade prices, I fitted belt, tensioner and guide pulley plus water pump and drive belt.
Still wasn't cheap but had a tensioner fail on my old 2.0 Ghia which wrecked all 16 valves and wasn't going to risk it on the ST.

Ford don't list as a full kit though for the ST170 - you have to buy individual parts. I understand Dayco do a good kit though, and well priced.

Good luck.