At 18" apart, your lights are approximately at quarter points, so personally I think that is ideal (from a visual perspective). A friend of mine has a similar size island to yours and has her lights at quarter points. She has 12" pendants and they offer plenty of light for the entire surface. I think the size will depend on the style you select. In my previous kitchen, I had a 60" island with only one pendant centred over the sink. It was perfect for us, as we also had potlights and plenty of sunlight (3 full height windows, w/ patio door).

Just my opinion on the shade size: Just from a "looks" standpoint, I think the cord or rod length should be at least one-and-a-half (twice or more is even better) times the height of the shade. Otherwise, the pendant might look shade heavy. If your ceiling is high enough this is probably not a problem.

I love your countertop slabs, they are stunning. Based on all the criticism I looked at your layout and I see a lot of positives. You have a sink for cleanup near the dishwasher drawers and stove, and a second sink for prep work. That sink is not far from the fridge, so you can grab an armload of produce and get right to work ... and as you work the kids who just want a drink or snack from the fridge can get it without coming into the work L. This isn't a studio apartment, it is meant to work for a large family and so yeah, you may need to take 2-3 more steps to get around but that is somewhat unavoidable. For lights ... maybe something like this if you want something bold that isn't adding a lot of color: Huddardton Forge Erlenmeyer Flask Pendant Just a thought. Congrats on the new house. Don't worry about the people here who enjoy shooting arrows of doubt and dismay without offering to help identify ways to improve things. Some people naturally look for flaws and love to point them out (instead of asking why something was designed this way vs that way). It can't be a fun way to live life.

This is why I always have the electrician run the supply wires in the ceiling, with plenty of slack. We wait until after the drywall is done to cut the holes and use remodel boxes. People can’t visualize. Even when you draw them diagrams. Or, do an actual real completed DESIGN from the beginning, with all choices measured and specified, and SET. Instead of winging it without the ability to visualize. Design BEFORE you do any demolition or building anything. Then the boxes and lights go where they need to go with no angst.