Most people that I know do add scent to the plastics just before the pour. This keeps the scent from being cooked out of the plastic.
I believe that Chris from Al's worms used kick'n bass, But he recomended Pro-Cure as a headquarters for scents. I tried the threadfin shad scent and it is much better than lure crafts scent. More than 10x stronger. He said the garlic is even more power packed too. When Im in need of more garlic I will be ordering from them.
Speaing of Chris I havent seen him around lately. Anyone heard from him?
As far as salt goes bulk buy on popcorn salt is really cheep, and you wouldnt have to try and grind it. But it could work. If you could spend about 20.00 and get a 50 lb bag ( I think thats what they said) and its already done, Is more uniform, consistant and done for you is cheeper in the long run than to try and grind a smaller quanty several times a day.
But if you have it, why not use it? When it rund out pick up a bag and give it a shot.
BTW, welcome to the forum.