Taj Mahal and any quartite for that matter is so dense that it is particularly prone to cracking without experienced fabrication and installation. Some cracks can be repaired satisfactorily, but not usually inconspicuously, and if the surface wasn't properly installed, you could be seeing more cracking in the future. You should reach out to your contractor immediately for warranty service. If the contractor prefers to replace rather than repair, you might consider a different surface to avoid the same problem given that the installer obviously did such a poor job and left it with no comment. At the very least, you should not use the same installer for any replacement if at all possible.

We used BM White Dove In different sheens on the walls and woodwork to complement the polished TM Counters (but we have natural wood cabs). Our kitchen has north facing windows with lots of green trees. We compensated for the low light with 3000K (the warm-ish colored not the blue-ish colored) LED undercab and in cab lighting and sconces etc. The updated kitchen doesn’t seem dark or gray now which I was concerned about. I would definitely wait until you have the cabs installed, the counter in and some of the lighting wired in before choosing the backsplash. I was very surprised at how my original white tile choices didn’t do a thing for my counters and cabinets. good luck!

Floorplan is helpful, but we also need to know how wide your aisles are currently (they look tight around the island?). Here's a quick idea (may not be feasible depending on aisle width) - it might look a little odd to leave that arch hanging but it would give you seating and remove the current barrier island. With the new opening to the LR, you could possibly close off that doorway next to the fridge (where does it go?) and/or partially close the opening between kitchen and breakfast (could be used for pantry space, etc. if necessary). I squared off the angled pantry but I was guessing at the measurements. You could leave the angle as-is with this layout, but the overall appliance arrangement can probably be improved by eliminating that angle (depending on those exact measurements). Or a similar idea with an island instead of peninsula, with the sink and DW moved to the perimeter:

I have these countertops and it depends on your color balance. every room should have light, medium, and dark tones. now dark doesnt need to mean black, but the darkesst tone in the room. for yu, it might be your floor or that maybe the lightest as we don't have sample pictures. If your floors are light, I'd recommend darker hardware and accent pieces. everything then would be very light and i would use a midtone (a color between your lightest and darkest piece) that has a bit of yellow or rust to it (though the countertop can be beige, gray, and white with a rust veining, it can also be green. So I recommend picking your exact slab of quartzite, because if you don't, you won't know which you will get. Anyways, my style isnt everyones, but this can give you an idea. The stone on the right has every color in the cabinets, back splash, appliances, and the countertop. So one of these colors, even in a lighter or darker tone, should work. If you can get samples of each piece and create a board for the room, this may also help you select the right color for you and your home.