As far as I know the futtock 'staves' were no rigid pieces. They used a piece of rope for that (the same as for the shroulds). That is also how they show it at the Vasa museum. Also: no catharpins in those days.
Question 2: I really cant help you there.
And number 3: again taking the reconstructed rigging of Vasa as guideline: no ratlines behind the futtocks.