What wires for a z-wave installation in a 1982 flat?

Hello everyone,
I regret to admit that I have no clue about electrics.
I am currently preparing for a major refurbishment of a flat I bought, a building from 1982 so all the electrics need replacing.
I have read a bit about the bypasses and have come up with the idea of using z-wave based equipment.
I can handle the set-up without any problems but I don't know if I need to give any specific information about the cables to the electrical contractor I will be hiring for the job.
I know I need to provide for deeper boxes to accommodate this contraption:
http://www.z-wave.pl/pl/p/Przelacznik-scienny-podwojny-bialy-Z-Wave-TZ66D/2

However, I don't know what about the wires themselves (are there any "weird" ones), the instructions for this switch include the wires:
L: Line voltage input
L: Switched load output
N: Line neutral
3: Auxiliary switch signal input

The first 3 I can guess but what about the fourth I don't know.

Thank you all in advance for your help and any comments on such a job and the system I have chosen (not sure if rightly).

3: switching signal input from additional switch

If you are planning a complex renovation of your installation, you should consider whether it is worth basing a pseudo-intelligent house on a radio solution. Such accessories are rather used in already made installations. The cost of additional metres of twisted-pair cable will of course come up, but you will gain a more secure solution, you will not be locked into the future, and you will not need expensive radio equipment.

I have thought about this too, and as I say it is entirely possible.
I certainly wouldn't be thinking about it if I were building a house. My scale is much smaller and I don't know if it wouldn't be form over substance.

I've also tried to estimate the cost of such an investment and I don't foresee a tragedy but to be honest I have no idea what the cost would be when wiring a flat.

At the preliminary design stage it looks like this:
Switchboard 1500 - 500 - I am thinking of a dedicated switchboard or a raspberry pi with an attachment
light switches 6 x 150 = 900
movement sensor, light sensor, temperature sensor 1 x 200 = 200
2 channel switches 8 x 180 = 1440
flood sensor 1 x 250 = 250

And that would be my starter that I will be aiming for. I will certainly start with the switches and switches themselves. Only after that will the other components appear.
I am more tempted by the solution of a control panel put on a raspberry.
Of course, I can see the disadvantages of this solution, but I also see one big plus, the possibility of connecting everything myself. With a wired solution, I'm afraid I might not be able to cope.

You are going to incur a very high cost, which would easily be sufficient for a small KNX-based installation, i.e. the full profession. If I were you, I would think about programmable controllers such as Siemens Logo, Eaton Easy, et cetera.

PS. I myself have a Raspberry version B at home for testing and I will tell you that it is a lot of trouble, a lot of tinkering. Besides, if something is for everything, it is for ...