Pfft, am I the only on struggling to reach MN these past few days? Seems to be a morning thing mostly.
Anyhow, enjoying all the pink and the enviable chameleon that is Flo.
WRT terrazzo floors, well I'd like some more info because for example black walnut is very different from European walnut and concrete comes in many shades. I'm assuming slightly ashy not the high gloss deepest rich walnut and a slightly deeper concrete to pair with it? Are countertops in concrete too? Appliances, taps, and hardware in stainless steel and/or chrome?
Essentially you have a cool and warm pallette going already by the sound of it, and the flooring will be a large deciding factor into which side has the edge. Since it's an extension I'm assuming there will be at least one wall with a large expanse of glass and probably a good sized sky light. Which means for most of the year, even if it's dead south facing, it'll be flooded with relatively cool light (as there's so much of it and life is pretty grey in Northern Europe). On account of that I'd be inclined to push for the limestone aggregate (provided it works well with the other chosen materials and finishes) as the flooring will be a large reflective surface due to finish and colour and the cooler colours will enhance the cooler light as well as making complexions look like death warmed over in the midst of winter. Born and bred Northern Europeans instinctively aren't big fans of cool light to begin with so it can also feel subconsciously uncomfortable, especially if the space is large.
WRT aggregate size, from my personal experience, smallest spaces like hallways and toilets work best with a smaller aggregate, medium spaces with few elements like a bathroom over 10m2 suit larger aggregate where it's the standout feature, large expansive spaces look best with a medium to large sized aggregate with a few larger almost oversized pieces mixed in just to give it a bit of scale, provided the rest of the space is pretty cleanly designed, it can't compete with too many other elements, a large kitchen island to break it up is fine, but various elements, level changes, etc can get pretty messy and then smaller aggregate is better suited.
Which brings me onto extra colours, variety, etc. I'm generally not a fan of opening up to option c,d,e, and f when a and b haven't been properly discarded. When there's a myriad of choices it's really easy to get seduced in wanting to explore it all in the name of interior design FOMO but it usually just tends to muddle up the decision process. In my view even though it's all terrazzo, options a and b are an entirely different species of floor than the additional options, the former is a clean seamless almost industrial floor with a strong horizontal presence at first glance that lets other elements of the design shine, whilst the further options are more of a feature in itself and is very much defining the space, in which case that should be dictating the material choices of the rest of the space rather than the other way round.
Saying that, the light flooring alongside the other materials do feel like they could do with tying together with a darker colour. I think it would be lost as a small element in the floor and better suited to artwork, feature lighting fixture, window finishings or similar. A bit of statement greenery also won't go amiss.