Update: After the advice on this thread, We went with the single tier. The island back was built out a little more to give us more room behind the sink. Everything turned out great. The Granite is Lennon which has whites, browns, greys, and some copper/bronze. Also, there have been a few posts lately about granite costs/overages and trying to reduce budget by going with limited slabs. If you want a nice uniform look, I would suggest picking out multiple slabs so you can get a nice match/book match. See below how my granite vendor accomplished this. Other experts on here can go into other details. I love the way everything turned out. Can't notice the seam in the middle of our island unless you broke out a magnifying glass. There is a seam right in the middle but you cant see it.

I have teak countertops in my kitchen. Done out of 8/4 planks, edge glued. I used biscuits and West System epoxy. I wiped the plank edges down with acetone just prior to assembly. The run of countertop as a whole is 30" deep by roughly 18' long, it's two separate pieces that overlap on the ends, one about 12' long, the other about 6' long. The overlap is because one countertop is a couple inches lower than the other one. I have an under mount kitchen sink, so the end grain of the planks is exposed to water at the sink. Zero damage. Been in for almost 20 years. No warping, lifting, curling, no separation at all on the glue lines. Finished with mineral oil. The oil holds up well, I try to renew the oil once or maybe twice a year, though I have gone several years without renewing it. I have another teak end-grain butcher block cutting surface as a kitchen island end cap. Roughly 4' square with one corner clipped on a 45, and 5" or so thick. The individual blocks are about 3-1/2" by 2" and assembled in a running bond pattern. Same assembly; I wiped the blocks down with acetone, then epoxied. No biscuits on that one. We do cut on it some, not a lot, but the cutting surface has held up perfectly. On the side or edge of the block, there's one break on a glue line, where the grain orientation of the two blocks don't remotely match up due to one of the blocks having wild running grain. The break isn't noticeable to the eye, but you can feel it when you run your fingertip along the edge. There's maybe a 1/32" lippage at that joint. Just enough to catch a fingernail on if you run it along the side of the slab. I've never bothered to sand it flush. Great material for a countertop. Been used and abused in a heavily used kitchen, and they still look pretty darn bueno.

@Alex P In theory, cabinets could be leveled to precisely the same height so that a countertop material would sit right down flat on top with no shimming. In reality, this almost never happens. Even with the very best technology in cabinetry leveling like using EZ-Level bracing which remains intact over time, you are still looking at having to shim a countertop of any type at least in a few places even in the best of circumstances. Regular cabinetry shims can shift over time depending on how they are applied, affecting your long-term stability prospects. For a countertop material that is already prone to cracking such as porcelain is, this becomes a great risk to try to shim that material with no underlayment for support, even at a 20 mm thickness. I would be more comfortable relying on the MSI guidelines for something like a small bathroom vanity countertop rather than a full kitchen where you will almost be guaranteed to need to shim the porcelain to bring it level across the largest run of your countertop area, thus leaving gaps between shims rather than the full support a subtop would provide. That is why you rarely see porcelain countertops without an underlayment unless it is for a small area like a bathroom. If you want the edge to be thin and polished without an underlayment, what this means is that you will need to specify your cabinetry to be constructed with full subtops and then somehow get them all perfectly level and ensure that there will be no shifting of the cabinetry or foundation in years to come, and then lay the porcelain down without shimming it if at all possible. Your idea of metal trim to cover an underlayment is creative, but remember that Schluter is designed to be anchored into grout, so you would need to be confident that you could secure it in an alternate manner before going that direction since you won't have any grout or tile adhesive in that area. I mentioned honed Absolute Black granite because it is much lighter than the polished type. Some varieties present in a gray color like concrete which is why your description reminded me of it. Soapstone also comes in a matte gray variety. I put soapstone in my own kitchen and love it, and it is considered to be a modern material for current kitchen design. Prepare for heartbreak if you do go with porcelain under any circumstances. Cracking and chipping with porcelain can happen, and it can happen to you, sometimes beyond any hope of warranty coverage. I liked the look of porcelain and its wear properties, but after much research including seeing cracks and chips in finished applications and talking to experienced fabricators, I decided to spare myself the risk. I have been thoroughly happy with the soapstone instead and recommend it if you cannot find anything else suitable. Even a honed marble like Danby would present fewer headaches for you than porcelain or concrete, I think.

@thinkdesignlive I had no idea that the blues I'd picked out had red in them. I have been in touch with a Sherwin Williams color consultant, and will probably buy paints from her/ get her advice about actual paint colors when it comes to that. She'd also suggested figuring out the countertop first, in order to get it to work with the floor, before thinking about paint colors -- and she was the one who actually mentioned (an unspecified shade of) blue to go with the floor. The other half of my kitchen has a lot of bright colors, so that's another thing to keep in mind. I'd prefer not to have a totally solid color -- after all, butcher block would look nice (right?) and isn't solid. In terms of less busy stone, what about a Aspen White granite or a quartz with a more subtle veining pattern? We've seen Taj Mahal in both quartz and quartzite and though it would probably work very well, hadn't felt drawn to it. I also am liking some of the quartzes with subtle veining (see the top left four little squares in the first picture in the original post) -- would something like that be too busy, and/or are there granite or other natural stone options that are similar (if we decide to go the natural stone route)? I also found this suggestion on Houzz of a less-busy granite that might work with a slate floor - thoughts? -- I do have the beginnings of an idea book, here and on Pinterest -- here are a couple of links to ones I particularly like: https://www.pinterest.com/pin/307863324533778336/ I love the blue cabinets with the slate floor! Although we are probably going with a stainless farmhouse sink. Notice the white-is countertop: wonder what material that is? http://pinterest.com/pin/15621929927201978/ Interesting how they offset the look with a blue/butcher block island and white cabinets. We don't have the option of an island as contrast, so I wonder how this could be incorporated. Thanks, @thinkdesignlive and everyone else!