Cheap attic conversion - How to insulate, what to consider?

A seal is still necessary on the wool, and for that the roof must be uncovered. Everything else is sheer nonsense

May I ask why the seal is absolutely necessary?

I confess (and am not ashamed of it) that I am an amateur and naturally still need to familiarize myself with the subject matter sufficiently before I even start to take action.

So far, however, I have assumed that roof insulation is only possible if the roof is completely covered and a corresponding rebuilding takes place, which is not an option for me for various reasons.

Therefore, I was interested to know whether it is basically possible to insulate without this "complete renovation." And some statements here show me that it is probably possible.

So once again, many thanks for the encouraging information. I vow to educate myself sufficiently before I get started

Is there perhaps someone from the district of Coburg here who already has practical experience in this regard and would like to support me with advice on site for the project?

Spacers between the battens (on which the tiles lie) and then the appropriate foil (there are various providers) glued between the rafters.
The roof does not need to be taken off. As I wrote, it is also professional and correct.

Some questions about that:
How should I imagine the spacers?
Is it only about preventing the battens from having direct contact with the insulating material?

Does this foil have to be glued between the rafters first before the insulating material is inserted, or is the foil the vapor barrier meant, which is glued from the inside over the rafters and insulating material after the insulating material is inserted?