Wooden beam ceiling construction, but how?

Hello,

we are currently completely renovating an old small house.

I have a few questions about this:

I would like to remove the aluminum-coated 100mm insulation and then install new 160mm insulation.
The ceiling, the top floor ceiling, has just been leveled with battens. Is it okay to staple the vapor barrier to the battens and then directly attach drywall on top?

Also, is it worth replacing the insulation?
Thank you very much