Everyone is asking for a porcelain slab fabricator close to where they live. What I did was search on Houzz to find local contractors with porcelain slab installations. Then viewing work that they did a few years ago for any cracking particularly around the sink faucets. I did not have good experiences asking the material vendor for contractors for other projects I have done.

I was discussing whether to go with 12 mm porcelain slab or not for my shower walls with the fabricator. The fabricator told me that the porcelain slabs on walls with shower niche will have at least 4 seams, 2 seams on each side of the shower niche to prevent it from chipping/cracking during installation. Not sure if this is true or if my fabricator lacks the experience and or tools to install porcelain slab on shower walls. Hoping someone here knows. Also, does anyone have experience with porcelain slabs on shower walls? Any chips at all especially around shower niche or shower bench?

Millworkman is correct. A large slab of concrete (regardless of exterior driveway or interior living space) needs relief cuts. These need to be planned for in advance and dealt with at the time the slab has been poured or shortly afterwards. The fact that your builder's 'slab people' didn't do such a basic thing - relief cuts - is questionable. Then to ask the same people to look at a cracked slab to determine 'fault' is working into the 'wonky' range. The last photo with the measure and the size of the crack is concerning. The other photos look rather innocent....but you never know with concrete. I suggest paying to bring in a concrete expert to examine the current condition of the slab, and the grade of the property...drainage, etc. If the builder used people who did NOT know to cut the concrete slab (to prevent unwanted cracks) then what else was missed or done poorly? At this point, I would NOT trust what the builder's people say until it is verified by a third party. As paranoid as this sounds, it is in the concrete company's (and the Builder's) best interests to say 'this is fine...don't worry about it'. It costs them less money if they homeowner believes them. And at this point, I would put the 'hardwood' flooring on hold. Because if the concrete has been cracking, it might be damaging the vapour barrier underneath...causing a WHOLE NEW set of problems with wood flooring. And besides...the slab must be FIXED before you lay wood flooring. Which means you need to bring in some concrete people to fix this anyways.

@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.