Tensioner and
timing belt can be had together for about half that price from Brickwerks, while
water pump is about £20 more. Sometimes you don't have time to get decent parts, and sometimes the stuff at the local motor factors is decent enough, but you will almost always find BW is better quality and value for money than other sources.
It's not necessary to change the water pump when the timing belt is done as it can be done separately, but it might be worth doing while it's in for work if you have the budget and it's not been done for a while. It sounds like your mechanic is suggesting it is done.
Coolant needs to be
G12 or later equivalent that meets
TL VW 774 F. You'll need 8 to 9 litres of concentrate diluted 50-50 to give the 16 to 18 litres of coolant required. There's a really good guide to properly bleeding the system
here.
Drop me a PM if you want a PDF of the JX engine workshop manuals for your mechanic to refer to.