I'd suggest the appliances forum as well- searching on there for ventilation/hoods is a gold mine. I've always read that you should go wider, but a lot depends on the power of the cooktop and how it will be used. We're going with a 36in Bluestar and plan to do wok cooking. With that we're going with a 42 inch hood.
I would think especially on an island you may want to go larger, but there are experts on this and the appliance board that will have more accurate information.
I wish you luck with your choice, the ventilation was the least fun, but very important part of our shopping. So many decisions.

Usually we say it's a nice-to-have if you can go 6" wider than your cooktop. However, with an island hood, it's more essential. That's because there is not wall or cabinetry around the cooktop to contain the smoke and grease, so you need more capture area than you would if your cooktop were against a wall.

Don't think that because you have induction, not gas, you need a less powerful hood. It is what you cook that should determine how powerful your hood needs to be, not whether you use induction or not. I.e. if you do a lot of stir frying, or fry steaks, hamburgers and fish a lot, you would need a more powerful hood than a family that does not.

Also, the more of a canopy shape your hood has, the better it is at containment. My preference is for baffle filters over mesh, because mesh filters become easily clogged and lose efficiency. But perhaps baffle filters are not available in island models, I don't know. You can get advice on this on the Appliances Forum.

Make sure your ductwork can handle the exhaust. Your exhaust duct for the hood should be 8" or 10" in diameter, not smaller.

In addition to what AKChicago posted - you should also aim for a deeper hood...27" is best...for the same reason as the wider width.

Also...a more powerful hood is usually necessary for an island (or peninsula) hood.

While one of the reasons for the extra width, depth, and power is the lack of surrounding cabinets and wall to help contain and capture the smoke/steam/grease/odors/etc., another reason is that cooktops/ranges in an island or peninsula are exposed to stronger and more numerous air currents so the hood above them will need to be stronger and bigger to capture the effluence before it spreads to the other rooms...especially if your kitchen is open to one or more other rooms.

While those thin, flat hoods may look "modern", they are not very good performers - they don't have the "canopy" that is needed to capture the smoke/steam/grease/odors/etc. to direct it to the fan and out.

Thank you all for the tips. Looks like I am starting the search all over again lol.