Hi Pam,
sorry I've not been to Cha-am for over twenty years so can't help with up to date info. The beaches in the area tend to be long strands, even 20 years ago there were quite a few condo units as the resort is one of the nearest to Bangkok, so popular with locals at the weekend. We were based in the main Cha'am resort area, here the water was a bit cloudy. Further south where resorts like the Regent Cha'am (now Holiday Inn I think) and the Dusit are based the water is clearer.

September is not the worst time to go but you may catch some rain which can bring out jellyfish. Cha'am main resort area had a good selection of restaurants especially if you enjoy Thai food. Hua Hin is just a few miles down the road which has a good choice of restaurants and a night market. Plenty of good site seeing tours to go on as well.