ᐅ Ceiling construction with wooden beams – but how?

Hello,

we are currently renovating an old small house from the ground up.

I have a few questions:

I would like to remove the aluminum-laminated 100mm (4 inches) insulation and replace it with new 160mm (6.3 inches) insulation. The ceiling, the top floor ceiling, has already been leveled with battens. Is it acceptable to staple the vapor retarder directly onto the battens and then install drywall (gypsum board) on top of it?

Also, is it worth replacing the insulation?

Thank you very much