Definitely don't rinse the salt off. One of the nice things the salt does is pull juices to the surface of the meat--not enough to dry things out, but enough so that when the steak hits the hot pan you have a nice protein-laden coating (it's called a pellicle when talking about smoked fish--not sure about steaks) on the outside to caramelize. If you rinse it, you're rinsing that right off.
If your steak was too salty, then just salt more lightly. You don't need a ton, as what you get on there will melt some and mix with the juices and spread out. I think I probably use 1/4 tsp or less per side, and some of that bounces off/misses. And you won't lose the crust with less salt--you won't even lose it with NO salt. It's just easier to get if you use the salt to pull some juices to the surface.
If you have trouble getting good salt distribution, use your fingers and sprinkle it from a little farther up--like 8 inches from the steak. That'll make it easier to get an even sprinkle without dousing it.
Kosher salt is pure, like table salt, but without any iodine and (usually) without any anti-caking agents.
Kosher salt crystals are also coarse, but flat, which makes them easy to dissolve or season/coat meat.
Unprocessed sea salt is simply coarse; the shape of the crystals (whole or ground) does not stick to meat particularly well and the impurities make it harder to dissolve properly in water. It doesn't usually have minerals added (unless it's a really cheap kind possibly made from pre-iodized table salt), it just doesn't have minerals removed like table salt.
Kosher salt and sea salt are definitely not the same thing. Kosher salt can come from seawater, like sea salt, but the "kosher" part is all about the size and shape of the crystals, not their source.
Sea salt is not a good idea for brining. It's expensive and inefficient, and by the time the meat is cooked, any distinctness of flavour will have completely disappeared. Some of the minerals may even burn, depending on the cooking method.
Instead, use kosher salt or table salt for brining and add sea salt as a seasoning afterward if you want. Using sea salt for cooking, brining, or other preparation is simply wasting it.
Best Answer
The reason people choose Kosher/Sea/Rock salt over table salt is mainly down to the crystal size and the lack of additives like iodine.
Kosher salt is less soluble and less dense than table salt.
The large crystals in these salts mean that unless there is a fair bit of water present they don't completely dissolve. This means it is less likely you'll over salt steak even if it's caked in crystals.
Table salt will dissolve with far less water present and will, therefore, get absorbed more easily into the meat.
Also the lower density means you can liberality sprinkle Kosher/Sea/Rock salt on things and even if it does all dissolve you've actualy added less salt than you would think. It looks like a lot but 1g of Kosher/Sea/Rock salt takes up a lot more space than 1g of table salt.
1tsp table salt would be way too much. I'd go for about half the volume of Kosher salt if you were dissolving it in liquid and maybe as little as quarter the volume if I was using it as a rub (as in salting a steak).