Ductless downdraft vent for island cooktop

It won't work like an actual ducted vent. The vent less basically uses an air filter and the recirculates the air back into the kitchen. It is up to you which option you choose and for you probably the non ducted route is best. Keep in mind more maintenance will be required, such as changing air filters (which isn't difficult). Also, it won't work as efficiently as a ducted vent, but should get the job done in a residential application.

I have only worked with commercial products mostly, but I would assume you would be fine.

Ductless is pure garbage. Ideally a vent hood is the way to go but I'm guessing it will block your view from an island type range.

Downdraft is not that great to begin with but to install a ductless is not a good idea.

I currently have a ducted down draft and I hate it. I will never have a house with one again.

ETA: Just realized you are building a new home. Don't go cheap or avoid "pains in the arse" because at the end of the day you have to live and function there and you want it to be right the first time.