Many here say it's advisable to get a hood larger than your cooktop, but many others of us, like me, have hoods the same width as our cooktops/rangetops and it works fine. If your cooktop is up against the wall with uppers to each side, that will help funnel everything to the hood...if over an island or is otherwise wide open above the cooktop, it could be nice to have a wider capture area.

--I'm not an expert on CFMs. 600 sounds reasonable unless maybe you're going to do an unusually large amount of meat-searing, deep frying, or stir-fry. Might be fine then, too. I had 525 CFMs in our last house, and felt it was OK, but sometimes could have used more power.

If you go over 600 cfm's some local codes require you to install a system with make up air. I would think that 600 cfm's would be more than enough for you, assuming you do "normal" cooking. Many on this site would disagree - there is a bias towards the hoods on steroids. The link I'm attaching talks a little about your cooking style and venting needs for induction cooktops.

Some people think that rhome410's point of having your hood 6" wider than your cooktop is just as important in adequate ventilation as the power the of the vent itself.

Here is a link that might be useful: FAQ #8 the induction site

I am installing a 42" built in vent over my 36" induction cooktop