I've been landing in Mozambique on the beaches for quite a while now. The grains of beach sand is too heavy to get a brown out so I don't think that is something to worry about. The sand does blow around alot so make sure no one stands close when taking off or landing.
The most important thing to take into consideration is how wet the sand is. Some beaches can be wet and solid as concrete. Others you sink in as you touch down.
Leaving the helicopter there overnight might pose a problem depending on how close you are to the water with the tides. I had a AS350 sink in the back part of the skids because with my luck I landed there with spring tide. The water didnt come within 20m of the helicopter but the dampness creaped underneath the sand towards us during the night. The next morning we had to dig a little bit
IMO I would say rather make a clearing further away from the beach and build a concrete pad. We actually just use planks that are about 3m in length and you place them so that the helicopter lands on at least 5 planks. The same as landing on a trolley.
Sand does eat up you tailrotor blades there so make sure you keep an eye on them. Also make sure you have a good sand filter fitted. The same we use when in the desert.