Could anybody give me a bit of advice pretty please

Ive had my audi a4 1.8t sport for a couple of weeks now and after about 10 days of driving the engine management light came on
i bought it private so have no warranty. took it to audi for a diagnostic which cost me £55.
3 faults had registered.
1. coolant temp sensor
2. thermostat problem
3. loss of boost pressure/throttle body issue

audi were very vague in explaining the errors and just printed me off an invoice saying over £800 please to replace the coolant temp sensor, thermostat and throttle body. great......

The car idles fine and runs fine. Although it takes about 10 mins for the temp gauge to move off 50. with the climate control off the temp climbs up to 90. the temp stays between 60-70 when climate control is on.

so.... after reading up on here ive realised that these are quite common things to crop on a4's and see that people have quite easily done the work themselves. so heres what ive done up to now...

1) replaced the coolant temp sensor(good job ive got thin fingers :-) ) cost me a little over a tenner and took me about 30 mins.
2) taken off the throtttle body and cleaned off any residue build up. there wasnt too much but there was some there.

What next. How do i know if there is a problem with the thermostat? could it be linked in with the problem with the coolant temp sensor?
will the cleaning of the throttle body be enough? can they fail?
do i need to clear the fault codes for the car to run normally again(as in not bipassing the coolant temp sensor failure)

i only did the work today so havent had chance to do a proper run. its done about 6 miles and the temp gauge just started moving off 50 as i got back. i left it running a further 5 minutes idling with the climate control off and the gauge moved up to 70.

what should i do next