Beautiful clean modern kitchen! You have a great opportunity to put your personal stamp on the space with a unique backsplash. As you've heard already there are some different approaches. I'd probably place the backsplash up to the wall cabinets and up to the base of the hood. Then continue the backsplash at the same height (18"?) behind the sink. Then place an inspiring colorful picture above the sink to break up the wall. Here's a picture with pendants that aren't too obtrusive. Having multiple levels of lighting at different lumens makes a more inviting feel to the space. I couldn't decipher your flooring, but you may also want to consider adding some nature elements like a type of wood flooring, wood stools, etc. Good luck! If you need software to plan out materials check out our Home Designer software: http://www.homedesignersoftware.com/

400mm sounds good! Did you go for a smaller pendant?

I would get a better chandalier with better lighting and IMO DRs do not have to be bright as they are mostly used in the evening.

The number you need for adequate lighting is dependant on the light fitting, its brightness and the angle the light will cover. The physical size of the fittings will also affect the number that looks best. Two very small fittings may give adequate light but look lost, while three larger ones could seem crowded. You may even find some very small fittings that work well as a group of six. Take into account the width of the surface as well as the length so you can ensure it is all well lit. You may be able to change the brightness of the lamp in the fittings to give a good work light in the number of fittings that look best. Avoid creating strong bright/dark contrast areas on a work surface. More overlapping less-bright light is better than few brighter ones that leave dark patches between them. Also consider whether there are other elements in the space that the group of light fittings could relate to, whether window mullions, cupboard doors, seating etc. If something else is creating a strong rhythm, decide whether you want to echo, or offset that or have the lighting as a background element that doesn't have a strong relationship to it.