There is no direct bus from Kunshan City to Qiandao Lake, you need to make a transfer at Hangzhou.
Bus from Kunshan long-distance bus station to Hangzhou: 0640, 0740 and 0850. it takes about 2.5 hours and rmb50. Seems it arrives at Hangzhou north coach station.
Bus from Hangzhou West Coach station to Qiandao Lake: 0600, 0720, 0750, 0900,0940, 1040, 1350 and 1210.around rmb45.

I think there are always package tours in china tourist cities, Qiandao lake shouldn't be an exception.

Thank you Jack for your help. May I know where do I buy the bus ticket from Tunxi to Qiandaohu? Do you mean the bus will take me to QDH and I can start sightseeing from there, no need to take another ferry from the jetty? Thank you.