I agree, do the timing belt too when you do the pump. Cheap insurance and you need to pull the timing belt anyway tp get the pump off so why not. I did the serpentine belts as well.
Personally I'd avoid a used pump simply because of the pressures on the bearings from the timing belt. I did mine at 120,000km and it looked and worked fine but who knows how long it would last. Why take the chance...
No issue what so ever with reusing the tensioner. Its a solid unit as long as you don't push the piston in too fast and screw it up when resetting it.
Cheers,
Doug