Where is the best beach on the island with nice local restaurants and a decent hotel?
Have a read about Ko Kut on Travelfish. Lots of useful information and the hotel really depends on your budget as prices vary. We are staying at Shantaa resort but may not suit you as not a lot close by. Peter pan hotel and a few others on Klong Chao (most owned by the same hotel chain along this beach) may be worth looking at otherwise further south near Ko Kut resort may also be an option for you. It took me a while to choose a hotel.
Have a look at Klong Chao beach. A handful of very nice resorts - Peter Pan / Wendy / Tinkerbell and High Season - on the beach and a few small restaurants and shops on the main road close by.