1

I think you've heard wrong! I'd say that the best way from AA-BD is with Sky or Selam bus.

2

I travelled by Selam Bus. Takes about 12 hours to reach. The bus is very comfortable. The ticket booking office is in Meskal Square.

3

I think you heard wrong too. Mini buses or shared taxis do not have a good track record for safety. I do use them however from time to time because they are more flexible for schedules and much more frequent. They are also very inexpensive but where safety is concerned the bus is a far better option. You can catch a minibus from the main bus station. Just ask around and you will be directed to them but keep in mind these are not formal which means they sometimes take alternate routes, accept oversize baggage inside the cabs and typically try to pack too many people in too small a space......and yes, they will take your chickens if you have any.

4

By road minibus is by far the quickest way to get to Bahir Dar. Just go to Merkato Autobus Terra and ask for one, the organisation is informal by western standards. You'll pay around 300 birr (if you don't have to pay a luggage fee), ride is about 6 hours as minibuses can travel much faster than regular buses.
Otherwise take Selam bus. You can book in advance, pay a similar fee but it's slower

5

Addis to Bahir Dar in 6h - that's suicidal!