This forum has an irrational hatred of stoves in an island. I feel more ambivalent about this solution. It depends a lot on the layout of the kitchen. There are situations where it clearly is inappropriate. But I have also seen stoves in an island that worked amazingly well. It's fun to have Teppanyaki inspired cooking right in front of your guests. Friends of mine have that, and it works great! Venting a freestanding range is much trickier though. In traditional kitchens, the upper side cabinets and the backsplash function as guides for the air that is being vented. Without these guides, the hood has to be a lot more powerful and has to have a bigger capture area. And that of course increases the need for an expensive make up air (MUA) system. Alternatively, you could contemplate a downdraft system. But you should realize that downdraft never works particularly well. It works a little better for induction cooktops (instead of gas). But it's always inferior to an overhead hood. I wouldn't recommend it for an open floor plan. These are all decisions that have to be made in a conversation with an experienced kitchen designer, as they have other implications for the rest of the kitchen layout.

Unless I am missing something a townhouse is an attached home and not stacked on top of other homes. It is not generally considered to be a multifamily dwelling - i.e. having multiple units within four exterior walls with shared plumbing stacks. Therefore plumbing lines aren't shared and bathroom and kitchen models are generally constrained in the same way detached homes or semi-attached homes are - i.e. most people for budgetary reasons keep toilets in same place and try to avoid major changes in pipes and drains. FWIW, I am in a high rise condo and converted my tub/shower combo to a larger walk in shower that followed the footprint of the original tub.

You need to draw a floor plan showing all the connected rooms with exact measurements. It's impossible to help with the pictures posted.

removing windows and putting in a door is easier than vice versa. remove the brick, frame out the area for the door, install. if you want to bring up the floor level,(what do you plan on doing w/the fireplace? you would have to redo it and the book cases) for the new floor, they would have to lay joists, sub floor, and flooring to even it out to the other. At this point I would advise you to replace all of that white tile and do the same flooring throughout the first level. can you match the wood you have in the other room? .Oh, demo of all that tile? 1-2 K (can't see how much you have) remove a window and install french doors, about 2-4K. building a banquette? have no idea. 1-2K? new table, custom made cushions, etc. I don't mind the sunken part. I'd do the french doors and close off that other door by the nook. would be cool if you could extend that whole side of the house further out another 6-10 feet. I'd rather do that than raise the floor level. i'd also widen your stair area leading down. on the living side, you could do something like this w/stair sides (little built ins) install a cool beam above it: or move the stairs to one side If you replaced your windows w/doors, you could do one large sofa, and place the two chairs as you come down the stairs. (that's why it might be nice to move the stairs off to one side, gives you a bit more space. or try this layout. you may have enough room to walk behind the other sofa in front of the doors. (if you could bump out that wall another 6' or so, it would be perfect!