What are the current counters, that would motivate you to spend a couple thousand dollars to get the same look? I think I'd keep those and just replace the backsplash with something you like better -- maybe something that becomes the star, like this:

Modern Charm in Highland Park · More Info

Then you could keep your natural cabinets and white counters, and paint the island something that matches a tone from the tile, like blue or gray.

Modern/Contemporary Spanish Kitchen in Blue and Rustic Alder · More Info

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A few thoughts on things you've asked about.

1. I see you seem to like the colour blue in your home. I can't think of a neutral colour that will go well with the natural maple cabinets but I think that perhaps a dark navy blue would look nice for your island.

2. For your counters i would choose a stone with more movement. I am not a fan of quartz and therefore don't have any specific colours to suggest but i do think that Fantasy Brown Granite would look lovely.

3. A farmhouse sink would look great however you may have a problem installing one as often it requires significant modifications to your sink cabinet. Usually the sink cabinet doors need to be shorter than standard to accomodate a farm sink.

4. Cutting down the corner cabinet will depend on how it was constructed. Often they are built as two separate cabinets. If this is the case then yes it is no problem to remove. If it is not then cutting it down will be much more challenging. I would have a cabinet maker do that for you if possible.

5. Pick your backsplash after you've picked your counters. Even better if you can wait until the counters are installed.

6. Handles- For a more modern look i'd look at brass or gold coloured handles

You can probably hire a carpenter to remove the appliance garage. That opened cabinet is clashing with the glass cabinet.

I wouldn't paint the island. if you want to keep your current maple as is, then leave it.

what you could do is do a darker top (like a soapstone) on the island and a whiter perimeter countertop.

why don't you go look at a stone yard and see what you like? take a cabinet door w/you.

find some hardware you like.

wait until countertops are in before deciding on a splash. (but remove the old one when the countertops come out)

if you want more room, modify that appliance garage.

Kohler Whitehaven has a drop in farmhouse sink that requires no cutting.