A few things wrong here other than the island placement. I would never have the sink and cooktop opposite each other . 54” is in no way large enough for a walkway behind stools that are in use. I agree that the overhang looks much larger than 12” steel supports are needed for sure even for 12 “ BTW architects are iften the worst KD s . A pantry outside the kitchen never makes sense.

If your only table space will be a banquette, keep in mind that while children love them, they get old fast for adults if you have to slide in/out and/or have to ask someone to move to get to the back. I think small banquettes are fine for very informal eating/visiting, but I would want a real table/chairs for sit down dinners, etc. As your children grow up, dinner time becomes more and more important (look up the studies). If you and your husband would be OK with sitting at the bench full-time, then it might work. Caution: Older people usually have a more difficult time dealing with slide-in (and island) seating, so if you have elderly parents/grandparents or you plan to age in place, then include that in your thinking/planning. . The next question is: Will all that you're planning really fit without creating a bottleneck or cramped space?

if the window lines up with the end of the counter, go just to the end of the counter. but are you going with tile all the way up to the ceiling? maybe you can attach a photo from further back so we can see the full wall? if you are going up to the ceiling, i would want to see the photo from further back to see what would be best.

That IS a little awkward. I'd look for very small molding trim pieces, paintable to match cabinets and sill, to go on that edge from the sill around the corner into the cabinet. Something like a L in profile that could cover the edges. If you have the chance to get it redone, have it end a few inches away from the window (like as far as the stool comes out to the side) and use a Schluter type of edging. At least caulk the edges with paintable caulk and ignore it. The big picture looks good! It'll only bother you when you're at the sink. :)