From what you have said, I'm not sure, but it sounds like you only have ten acres for the animals to graze. With ten head of stock on ten acres of coastal, you are probably going to be at high risk for overgrazing. About half that number is the max that I think you should have, unless you are going to use heavy supplemental feeding year-round. I would suggest that you reduce your herd. In my opinion, one of the most unhealthy things for an animal is to have it in overcrowded conditions. I know it may seem like the animals have alot of room, but they like fresh grass to graze, that hasn't had their waste product passed on it recently. I believe you also increase the concentration of pests when you concentrate your herd. The advice to rotate grazing plots is good, but ten animals on a fraction of an acre will probably reduce it to dirt in two or three days.
You might consider growing a cover crop in the winter months for additional grazing. Annual rye grass might be a good choice, but try and keep your soil in good condition. Have you ever thought of growing your own feed? It might be more feasible than you think, however, this would mean that you would have to either reduce the number of grazable acres, or take in some land that was not grazable before as farm land. The animals can eat much of the stubble, though, and some grains can be left on the stalk for animals to graze at will.
It will be interesting to hear how you work your problems out. Please keep us posted. I hope our advice is worth more than you paid for it!
Best of luck