Different gardeners have different opinions for using even organic methods. There are many recipes for the recommended ratios of many organic sprays that you can find all over the internet. Some even suggest 100% milk. If you aren't sure of the recommendations you receive, follow up with research until you find sources that you can trust.
Anyone with the capability of getting text into a computer can publish a web page, have a blog, plagiarize another source, have a typo, or provide misinformation. In the end, you have to decide which is safe for your plants, how often to use any prescribed method and also evaluate the effectiveness or harm of the options you choose.
How often you use a treatment ties directly into what ratio of the treatment you use as a main factor. Other factors may include your climate, time of application, and whether the plants are getting proper nutrients and environment to make it more susceptible to powdery mildew - so treatment may not work effectively long term. Researching why a treatment works, at least the basics, and why "more" is not always better will probably clear up a lot for most gardeners. Or at least make it easier to determine the voice of reason you want to follow. You can always opt to switch treatments if one doesn't work or causes more problems.
As far as the milk goes, you can use it on other plants besides your tomatoes - most plants that have a smooth surface are ones that I'd use them on. I'd avoid it for plants that are very hairy or have hair-like leaf textures like lamb's ears. But again, knowing why involves a bit of research. Some recommendations are to avoid getting too much of the milk in the soil - will make those roots seem even more tasty to some underground critters. Epsom salts can be used in the soil, watered in. Different schools of thought on how good that is though, especially with the frequency that it can be safely used on the foliage.
"Love all God's creatures, the animals, the plants. Love everything to perceive the divine mystery in all." -Fyodor Dostoyevsky