A few questions about my electrical installation/ consumer unit

[Jurghh]

Hi All. I've been a lurker for a while, though never in this forum, but this is my first post. I hope to be able to contribute and help others in the future.

 

So here goes... I'm redoing the kitchen in my BKK condo and I want to add 4 new circuits (sockets & microwave, dishwasher, oven, water heater). The CU is located in the kitchen. I've already chased the walls and installed conduit & back boxes etc.

 

Initially I planned just to add standard MCBs like the ones currently installed but now as I've learnt a little bit more about electrics I think it's better if more or all circuits are RCD protected. Currently only circuit 6 (three down from the right, blue wire) is protected by an RCD. This is the circuit for the existing sockets in the kitchen. So i've got a few questions i'd be very grateful if anyone could help answer:

 

1. What would be the best way to add RCD protection given the layout of the 3 phase CU? To all circuits or is it less important for others? 

2. Could for example all of the existing MCBs be swapped out for 1P RCBOs? The Siemens ones have functional earth wires that need connecting. RCCBs an option?

3. Why did the installers use a 2P RCBO linked to an MCB to add RCD protection to the existing kitchen sockets instead of a single 1P RCBO?

4. Why did the installers break the colour pattern and use black wire instead of red for the bottom left L2 circuit?

All of the companies I've had round to do a survey and quotation haven't actually offered a solution in any detail.