It’s a large room, it doesn’t seem excessive to me. They’re all for different functions? Dining table for eating, window seat for reading, sofas for tv, chatting etc and stools for talking whilst someone is cooking etc.

Having said that it can be dangerous having stools behind a hob

In the extension we're currently having built, we will also have lounge seating, a dining area and breakfast bar seating. The different seating areas are for different uses, so consider how you will use the space. In my situation, I envisage the living room seating (sofas) to be for relaxing, the dining chairs for eating together as a family (which we do every evening and often lunchtimes too), and the breakfast bar will be for my (teenaged) children to eat breakfast and snacks. Which they do every 5 minutes because they're teenagers... Your window seat is a lovely addition and I imagine it would be used for solitary reading/drinking a coffee etc.

You don't say whether you have children/what ages they are, but I think breakfast bar seating is a good idea at any age as it means you can get on with things in the kitchen but still chat with them/supervise homework/give them snacks or whatever. Plus I'm looking forward to chatting with friends (when we're allowed again!) while I cook. I'd rather they have somewhere to perch than have to stand up around the island.

Lots of people don't have seating at their island and that's fine too, but it really all comes down to how you like to live (or how you envisage you will live after the work is done). I know for sure that my kids would wander over to the sofa with their snacks as it doesn't feel right to them to sit at a dining table on their own for a snack - and I'd rather keep their crumbs and sticky fingers in the kitchen area!

It's not excessive. As mentioned above, they all have different functions.

Go for it....we have children and there's always need for an different seating areas to match the mood...