I don't have one in my island unit. I had one many years ago and didn't think it was effective. This afternoon I've been out to quote on kitchen worktops and they had a wide chimney island extractor over their 5 ring gas hob. To me it stood out like a sore thumb. I certainly couldn't get used to it (especially as a person who doesn't have or like them). I felt as though I would bash my head on it. Based on that I'd opt for something in the ceiling so it's not blocking any view.

https://www.planningportal.co.uk/info/200130/common_projects/34/kitchens_and_bathrooms/6 This advice says that you have to have an extractor if you don't have a window to open. I think that an extractor helps complete the look even if you don't need one. If you have a chimney extractor you will find that the ceiling fixings are designed for a flat ceiling thereby necessitating a bulkhead. Alternatively you could put in a bigger bulkhead with a flush extractor built into the boxing. My preferred option would be to have a statement recirculating extractor with an extra extractor somewhere discrete above the cabinets on an outside wall to vent if cooking something very fragrant.

Is the cooker planned to go against a external wall? You have a few options but it sounds like your steel beam might be right in the way of the duct if it's going straight up. If it's set back and you don't have another floor above, the duct can easily go through the roof. If you have a second floor above then it's more difficult. But there is plenty of ways you can duct out the back wall without wall cupboards. for example the cover for the ductwork can be placed all the wall up to the ceiling even when the duct has taken a turn out the wall. There are contemporary looking exhaust units that will cover the turn straight out to the wall, with no obvious duct work on show. Or you can just get a pop up exhaust or a flush ceiling mounted one. The latter two in my opinion aren't as effective.

Hi, Airuno do a couple called the Slimline Classic and the Eclipse. The motor sits between the joists and the body of the hood sits on the ceiling. The motor can be rotated 90 degrees so you can duct across or along the joists (although a little shaving is required if installing across joists). Alternatively in the budget range, there is the ViandPro Aria. This will sit flush between joists at only 207mm high, but can only be ducted along the joists. So if your joists run the opposite way to the hob, this won't work.