I'm not familiar with EU situations, but typically in the USA it works like this:

1) They will ask for volunteers and offer a certain voucher amount. If you scramble to the desk to be first in line you can ask about reaccommodation. Sometimes they know exactly what you'll be booked on, sometimes not.
2) Depending on the situation, they might confirm you then and there, but more likely they will tell you to wait to board until they know if they need your seat.
3) Probably (I have no experience here) they will start by offering something less that the EU requirement, but they may well go higher, because they would rather pay a few extra euros to be able to say that no one was bumped against their will.
4) Just because the flight is filling up, don't assume they will overbook. If there are 200 seats on the plane and by 3 weeks before the flight they've sold 202 seats, they can stop selling it.