This all depends on the weather, e.g. persistent rain will dull the thatch quicker, but usually a roof will not fade until 6-9 months after completion.
This all depends on the area you live in and the local thatchers rates,as these can vary massively. An average sized cottage should cost around £10,000 – £14,000
The chimney, including the pot, should terminate at least 1.8m above the height of the ridge