Hi i have my flight on 11th june early morning at 7am so i have to be there at 6.30am. Is there any ferry + bus to airport at that time?
You better go day before.
As suggested you should spend the night on the mainland.
what about bus and taxi availability in town in order to start early and how much they charge
I don't know the cost of a taxi. It's a good idea to arrange one beforehand. Perhaps you should look into hotels near the airport, it will make your life easier. Note that journey time from either Surat Thani or Don Sak pier is about 1.5 hours.