1) Best time of year: from 1 November to 1 May. My pick--Feb/March/April

2) Best sites: accessible from liveaboards to the Similans. Typically 4d/4n. But we can also do land based and have daytrip diving. We can dive for four days on day boats (2, 3, or 4 dive days) and not do the same site twice. We don't have dedicated dive resorts at Phuket.

3) Numbers: we don't need 10, but if we have that many, we can get cheaper deals (half charters, for example). However, with any number we can go. All kinds of price ranges are available from super budget to super luxe. You get what you pay for, in relative terms, though. Cheaper means shared bathrooms, for example, and no Nitrox fills.