Imagine it as two houses of parliament/government. The "upper chamber" has longer terms, and so different duties, to the "lower chamber". AIUI, the Board is responsible for (OTTOMH, YMMV, E&OE) some of the tasks Nokia were previously responsible for. Primarily, that means finding funding sources for maemo.org. The Council would be responsible for representing the community to the Board, and - with six month terms - be more reactive and deal with less financial, more operational tasks. You're probably right, there probably isn't a need for both governance structures - but I'd be wary of switching straight away.
So I'd propose option 4: 4. Election for new Board when the community is happy with the proposed governance model. Councillors can stand, and next Council election can still happen as before (not later than 6 months from the last election) if it needs to.