Present bread baker at Bar Tartine in San Francisco. Past pastry at Bar Tartine and Summer Kitchen. Baking all over California and beyond.
As for salt- salt should be added once the curds have drained. It's true that adding the salt earlier will change the moisture content and texture of the cheese. It will also drain out with the whey if added earlier, changing the saltiness and flavor of both the curds (less salty) and they whey (more salty.) Adding salt after draining make easier to control saltiness.
Quick cheese like this is sometimes called mistakenly ricotta- true ricotta (meaning re-cooked, in Italian) is actually made from the whey from the first round of cheese-making, re-heated and with more acid added, to precipitate any remaining curds from the whey. It's not a big deal to call this quick cheese ricotta- lots of people do- I just like using the term queso fresco for clarity.
A bit about the egg whites being free of yolks- back in my early pastry assistant days I tried to whip some whites that had a dribble of yolk in them. I whisked them forever without getting a good foam, and then they went straight to grainy. My chef immediately asked if they were perfectly clean (how did she know?!) and I had to own up. It's absolutely conceivable that I had done something else wrong, but ever since that incident I've adhered to the rule of only using clean whites.
The same concept holds true for all fruit; the most important thing is to choose fruit that is *just ripe*, and if one or two of those peaches are a little extra firm it will only help the flavor and texture of the jam.
Best of luck!