Himalayan salt is not really from the Himalayas, but from the Salt Range, which is nearby -not exactly 'Himalayan snow melt' (in fact an underground salt deposit from a sea that dried up hundreds of millions of years ago).
It has a bunch of impurities (or 'minerals'), which make it pink. It had no commercial value until recently when it became popular for Instagram. That's the value. It looks good in photos.
Salt is iodized for public health reasons. https://en.wikipedia.org/wiki/Iodised_salt#In_public_health_initiatives
Kosher salt is coarse and lacks iodine. It's for koshering meat, but the coarseness is good for some purposes (rubbing on meat). In the UK you can't buy it very easily, but you can buy coarse salt that's functionally identical (in that it's coarse and salt).
All work the same way. A fine salt and a coarse salt is handy to have. And a scale with at least 0.1g resolution to accurately measure them. Any time you are dissolving the salt, they are all identical, just make sure to weigh them - measuring cups and measuring spoons are bad.