Absolutely VENT OUT. With an induction you will be able to boil water in less than 30 seconds and stir fry at high heat. Do you want all that moisture and smells lingering and gunking up your brand new cabinets? A non vent range merely recirculates moisture and smells (think you burn something). Venting it outside takes it out. Whether to go straight up or out the side depends on the unit and its pull and that question should be left to your contractor after you decide on the unit.

The more bends in a venting system the more CFM you need so I would goup as straight as possible. Ventless hoods have a filter that needs to be cleaned on a regulas basis and the only time I use one is in a condo or a kitchen where venting out is not possible they are not mich better IMO than microwave ventless hood.

Vent UP and be sure to get a proper sized hood...6 inches WIDER than your cooktop = 42 inches.

Why do you go 6 inches larger? This is the first I've heard of this. Is it code or suggestion?