What else should I consider while replacing the springs?

I can imagine:
new rods
new valve seals
new valvecovers seals
new spark plugs
new (lighter) valve retainers
new (lighter) valve caps

Should I try rockers with a bigger ratio? (1.8)
Or is that a lost of time/money? The engine is supercharged and is 100% internally stock.

If the pushrods are still true I would not worry about them
Yes select the spring type you want and go with new lighweight retainers and keepers.
Also new valve stem oil seals.

Valve cover seals are reuseable so if they are not leaking you do not have to replace them

You really need to 1st choice what type of spring you want to use.
I find the dual springs that the inner springs tend to break as you can see from the photo when I changed mine.

The springs used for the L92 ( shown on right) seem to be a good swap and are the beehive type that use a smaller and even lighter retainer.

With a supercharger and as old as the stock engine is I would not go with higher lift rockers.

Are the L92 spring dual?
Is it OK to install single springs? I was thinking this was for safety in case that one spring brakes the other one would avoid the valve to stay low and hit the piston.

Look at the image above, the spring at far right is L92
You notice at the top the spring is smaller, like a beehive shape.
They are single springs but because of the design are as good or better then the dual spring.

The inner spring of dual is not for strength reasons

Fine, thank you.
Let me take a look at the engine...

Roght now I'm not in the mood to remove the engine and take it apart nor remove the heads with the engine still in the car.
Is there a way to understand if the lifters are damaged without removing the heads?
Same for cam, rods and crank bearings.

So far I checked everywhere with a sthetoscope at idle and revving the engine. But the noise appears only with a little load and while driving. As long the car dosn't move I can't recreate the noise.
The noise appears after about 2000 rpm.

I also remove the injectors plugs one by one to see if the noise changes depending on which cylinder isn't firing, but nothing changes.

I would assume of lifter is damaged it would not pump up and that pushrod would be dry.
Also that pushrod could be sitting lower then the others.

I would think if bearing or rod damage the noise would be heard all the time

rushrod... you mean pushrod? (sorry, my engine slang is pretty poor)

Sorry, my screwup, and corrected

Is there a way to check the lifters without removing the heads?

The lifters are spring loaded so with rockers off all pushrods should be equal in length at their tops.
If not then the lifter is collapsed and will not pump up

With rockers on and with valve cover off and engine running you should see oil pumping out the tops of pushrods.