This is very similar to a detail I am using on a house I am designing. In this house the screen behind the woodburner is a pre-coated steel corrugate. The manufacturers are happy with the temperatures the paint will be exposed to in this situation. Talk to the suppliers of mini-orb to confirm it for your situation. To function as a heat shield the steel needs to have sufficient ventilation space behind it, so needs to be fixed on heat resistant spacers and have sufficient openings top and bottom of the screen to allow the air to flow freely. This can be achievable with sufficient perforations or with clear openings. You will need lining such as plasterboard behind the screen. The detailing of the edges for the screen will affect how the screen works with your design, so think that through.

my understanding of how a skillion roof works is that it will actually move air the other way and vent on the high side. So you can build level walls and put a row of louvres above the wall on the high side for ventilation. You will need windows or vents on the low side too to bring the air in.

One of the issues with cooktops in the island is that you should have a range hood above - and pending on your ceiling design this may not be achievable or wanted. Also note that Australian standard states that all cook tops need an isolator switch within 1 meter of the cook top (normally I would put it as part of a double GPO on the splash back close to the cooktop - this can be problematic with an island.) I like to put prep bowls in the islands, but generally leave all main sinks and cooktops in the main kitchen bench, having them with a splash back behind is a lot more practical when it comes to cleaning.

the reason i love my new induction cooktop is the timer!! put a pot on the stove, set the timer then wander away knowing that the timer will save the saucepan from destruction...don't know about the cost of running the induction, only used for minutes every day so no appreciable cost issues..Love the new down draft exhaust fans and would happily pay extra for one in an open plan kitchen area if you expect to use it while cooking and trying to talk at the same time...it can't easily be added later so i suggest you economise elsewhere...good luck with your new home