are you applying for a single entry 60 days tourist visa? or any other type of visa?

you should read the instruction of your embassy; for example at my embassy, you only have to provide proof of accomodation for at least half of your stays

regarding the list of city to choose from: Koh Samui is probably not among them. try Surat Thani (province name), Chaweng, Lamai, Nathon...