Larry,

The lime is added one time and will last the season. Gypsum and epsom salts are not used in the 511 mix, but in the gritty mix. Al has an explanation of why to go this route with the gritty mix so I won't detail it here. The gypsum supplies calcium and the epsom salt supplies magnesium. For the 511, it's just lime to add both, skip the gypsum and epsom salts entirely.

For the 5:1:1 mix only:

1 level tbsp of dolomitic (garden) lime per gallon of soil
or
1/2 cup per cubic foot.

Don't worry about gypsum or Epsom salts unless you decide to try the gritty mix.

A full understanding of the thread I'm linking to below will help you quite a bit.

You already understand 'why' (reread your own post). How often - when you make the soil. It's best if you make the soil and keep it damp for two weeks before you use it, but not the end of the world if you use it right away.

Don't worry about how often. You won't need to add more of a Ca source until probably the third year, and that's really pushing a soil. We can talk more about how to handle the whole Ca/Mg thing in the second year once you understand things better. Deal?

Al

Here is a link that might be useful: More help