The things on the base of the tree are aerial burr knots, the rootstock is trying to sprout roots above ground. It sounds like the tree was grafted high. They don't really hurt anything other than giving bugs a place to hide. You could mound up dirt against the trunk, but I don't know how high they go. The leaf problem could be an insect like leaf miners or caterpillars instead of disease.

I had some for about 3 years, came back up each Spring, but now it's done. Don't know about the soil, because I always kept it in containers. (I had both the white and the pink.) I don't plan to replace it since the deer love it. I can tell you that the wild native variety (the flowers are much smaller) grows all around here and it doesn't seem to matter what kind of soil it's in. It grows in the natural woodland topsoil, which should be acid, yet it also thrives right next to the roadside which is crushed limestone. And it definitely doesn't get pampered with water and fertilizer.

From your description, doesn't sound like anything is wrong. You still have lots of flowers. That happened to my tree too. Probably just too many flowers for the tree to support. The timing is different than for me here. I just got done eating the last fruit, and you're just starting.

I do something similar to what John suggested. I use either a metal or metal mesh tea ball for herbs when I'm braising anything or making soup/stew. I fill it with dry bay leaves, whole peppercorns, and anything I want to add. It works fine. The flavor is infused throughout the entire dish, but there are no bits & pieces to pick out. I can understand about rosemary. Although I love it, the flavor is strong and the leaves are thick & sharp. Another suggestion, since I'm doing low salt too, is to find a good brand of flavored olive oils. At our local farmers market, I buy Sciabica's brand, and I think Annie purchases their regular EVOO. I just drizzled a bit of their lemon oil on a kale salad. I love their rosemary oil. Same with the garlic oil. The flavored oils are not really cooking oils but are great drizzled on vegetables, salads, or as a finishing touch on any cooked dish. Good for dipping bread too. Plus there's no sodium. Here is a link that might be useful: Sciabica's Olive Oil