Apartment wiring for beginners

Due to unfortunate circumstances a loft extension is about to happen: a living room, a bedroom, a kitchen and a toilet should be built on area 80 m².
A distribution box with breakers was used by an electrical installation company, and is located in the this area.
I have 2 connectors for lighting circuits and 1 Connector for power.
What would be useful-living room and bedroom a breaker and kitchen and WC on the other, or should rather have the living room with TV, PC and stereo a circle?
Can I switch all outlets (about 15 pieces) within a circuit serial?
The line will be up to 30m long at the longest point-wäre it 2 da sense, 5mm square to use wires or rich 1, 5 mm²?
The lines on the one hand in hollow walls and in the ceiling between the insulation and plasterboard should be laid.
And now a Commissioning jobs  of understanding:
With the light switches I turn on just the "live" wire, on the other hand, the lamps are also neutral and ground connected.
I should move there a 3 wire cable and also with neutral and the misuse of the light switch grounding or it would be better, with a 1-wire cable for the switch to use and the way back from the lamps to the fuse box a 2-core cable (neutral and grounding) directly to tread?
So away: 1 wire on the light switch.
RETURN: 2 wires directly from the consumer to the fuse box.
So, I would need a 2-wire cable, No 4-wire between the switches for the 2 planned Exchange circuits and save much cable anyway.
Then anyway I need a 3-conductor Sockets.
You have good advice for someone who is running such a wiring harness for the first time on what I should pay attention, what must be, what is important?
I have a clear view, theoretically concerning circuits, circuits, operation, basics, etc. I trust me also, to the attic, and everything I miss about a course, as it specifically runs the house wiring there it as a recommended reading?