Well to be honest that kit is a waste of time, the belt is contitech, isnt the best and pretty cheap to get hold of from motor spares place. You want GATES POWERGRIP Kit which is OE ORIGINAL on most cars such as vw audi skoda bmw vauxhall ford, most things you can think of. but defiantly get the FULL kit.
The Full cam belt kit for GATES is around £ 80 85 Last time i brought one.
You can also change the alternator/auxilary belt, as this has to be removed to do the timing belt, but it can be done at any time anyway it takes 5 minutes to change so its up to you really. i didnt change mine, didnt see the need yet. wasnt cracked or damaged or squeeking so i left it.
You dont need a new thermostat, or thermostat housing. Why would you need that to replace the cambelt... you wouldnt change the exhaust at the same time would you?
The camshaft and crankshaft seals can be changed for pennys. Just get them from the dealers. Can be changed but guaranteed they arnt changed at the dealers when they go in for a cambelt change.its just peace of mind to know the seal wont leak and put oil onto the the cambelt.
water pump can be purchased from any good car spares like GSF, for £25 for a metal impellor one.
Think that might save you a bit of money.. Around £ 120 max for the parts and 2 hours labour for the job. Can be done for £ 200 easily at a good independant garage, timing belts on the 1.8t are easy to do compared to some things out there so dont get ripped off. Get your own bits and ask them how many hours labour. Most places £ 40-50 hour.