The recipe calls for 1 2/3T Kosher salt. I know there is a big difference between the various brands of kosher salt, can you specify the kind or...

Yes, different salts occupies different volumes.
1 teaspoon flake salt (Penzey's) weighs 2.9 grams
1 teaspoon coarse salt (Kosher) salt weighs 4.8 grams
1 teaspoon table salt weighs 6.0 grams
My preference is always weight in preference to volume measure. But to weight salt, you really need a scale that weighs to the milligram; my digital scale can't do that. I am tempted, but can not justify the cost or the counter space for a specialty scale. Hope you find the values above useful.

If you use another salt, try 1/2 the amount given. The kosher salt may be indicated to dissolve quickly, so standard table salt or finely ground sea salt would be my preference.
For Diamond Crystal Kosher Salt, 1 2/3 Tb has 5600 mg sodium; it weighs 14 g. French Atlantic Sea Salt, in 14 g (this one weighs 1 g per .25 tsp -- other salts will vary), has 4620 mg sodium and measures 1 tablespoon plus 1/2 tsp.
How much salt is needed for proper yeast activity? How much for
flavor? At the lower sodium number, each piece has 192.5 mg sodium -- is that OK?
I wonder why the amount of sodium differed by weight? I thought it's supposed to be closer, but this is how the labeled numbers worked out.

I looked it up in her cookbook, but she doesn't specify a brand. I'd use Diamond Crystal kosher salt-- it tastes less salty than Morton's and 1 3/4 T is a lot of salt.