I’m pondering a downdraft induction job too for our upcoming Reno. Hopefully someone answers!

I recently purchased a NEFF induction cooktop and NEFF 60cm oven which is installed underneath. not sure it's a downdraft cooktop? does it have a special range hood?

The downdraft induction cooktop has the 'rangehood' extraction system built into the cooktop itself. Something like this https://www.neff.co.nz/productslist/rangehoods/benchtop-installation/integrated-cooktop-ventilation/T58TS6BN0

Just had a look at the specs. Should be ok. Bench depth should be around 700mm and height maybe around 950mm with 100mm kicker height. Depending on how you wan to run the duct.

sorry cant comment on the specific downdraft induction cooktop you are considering but can highly recommend Neff, they are a superior product and I'm sure if you can make it work you wont be disappointed.