Hi Brittany, welcome!
As for point 1, if you can stay below the whole time, thats definitely better. Do you have a watch linked to your HRM that you can set to beep at you when you cross from Z2 to Z3? Thats what I do. Either that, or just walk the hills. Its definitely better to stay below that threshold, but its not like some magical line you cross where instantly you’re doing harm.
As for point 2, that seems like a great plan! I would also throw in, especially as a runner, you should do some strength training, which I see you mentioned. Maybe you could view it as a mini cycle of max strength + base building between now and September.