On day 3 you were probably tasting the bacteria that forms in the early stages of starter creation, and that early bacteria should be overtaken by the yeast and long-term bacteria at the point you're at. At this point, you've probably got a good growth of yeast, but the good bacteria takes longer to settle in, and that's what gives you the traditional sour taste. I go more by sight and smell to tell when it's ready to leaven bread on its own - if you're using a 1-1 ratio of flour to water, the mixture will be loose, like batter, with a bunch of bubbles, and it'll smell almost like beer.
I've never used a dough scraper, and while I do like my banettons, they're by no means necessary. They give a nice design on the crust, and it's nice to have dedicated proofing bowls if you bake a lot, but regular mixing bowls definitely work as long as they're the right size. What kind of issues are you having transferring to the oven?