My kitchen is similar to the one in that picture and we've had oak worktops. Even though we also opted for a caramel bamboo flooring the room is still very bright as we've kept everything else neutral. It depends on the light and shape of your kitchen, but a dark worktop won't necessarily make the room gloomy.

Sensa is a natural stone so it could have unpredictable veining. However if you love it your worktop fabricator will probably let you inspect the slab before they cut it. Neolith is a sintered stone so much harder and more predictable. It will have a plain edge unless you pay extra for a dropped edge. Personally I think that if you are considering Neolith you should be considering Mont Blanc which is a similar pattern to the Sensa you showed. And in my opinion these products look more natural and expensive if you choose a satin finish rather than a glossy one.

You definately have the drop for a more statement shade in the staircase. An option would be a shade that allows light upwards as well as down, but please avoid a chandelier! I think the fashion for chandeliers has past and they are a bit cold in their feel and not welcoming cor a hall. Something with fabric texture could work well, or one of those petal shades.