Disclaimer: I’m no expert

You’re probably getting conflicting advice because there’s no one answer. But, I’ll give it a shot…
1. At lease three weeks before turning soil is my preference. This ensures that not only does the vegetation look dead, but the roots are completely dead as well. It just makes things easier. It’s particularly important if using a tiller.
2. All three are feasible, depending on different factors, but you may as well incorporate it into the soil when you work it.
3. That depends on how your soil works. If it’s soil that’s never been turned over before, I would figure a minimum of two, possibly more. But, your weeds/grass may not be as thick as they are around here.