Does yeast use the salt in the ferment

With all due respect to them, the health service doesn't have to eat the results of their recommendation. Bread without salt is nigh-inedible, and the salt isn't just for flavor. Reducing it also hurts the texture.

To quote On Food and Cooking (page 535): "Though some traditional breads are made without salt, most include it, and not just for a balanced taste. At 1.5%-2% of the flour weight, salt tightens the gluten network and improves the volume of the finished loaf."

This means that a less-salted loaf will be denser and less chewy, and an unsalted one even more so. Now, you can knead more to compensate for reduced gluten development, but it still won't be as good. Having baked and eaten bread without salt due to a hung-over cook forgetting to add it to the dough, I can confirm the changes in texture. It also seems to rise differently and overproof faster.

Oh, and it also tasted like cardboard. But again, the health service doesn't have to eat the results of their recommendation. I could go on an hour-long tirade about the culinary atrocities committed in an effort to reduce sodium.

Salt (Sodium chloride) is salt. As a topping, flakes are commonly used purely for presentation purposes only. The taste is the same, but gets more intense as the salt particles get finer, so use less if the salt is in powder form

As an ingredient, use any form you are happy with, and is economical to use. Once salt is dissolved into water it will be identical to any other form of salt

For health reasons, finely powdered salt is preferable as much less is required to impart a salty taste