Redoing “pro” shower install 2 years old

The guy used cement board and red guard

He did use cracked tiles, he used only grout and no caulk

No waterproofing on window surround except redguard on good, tile was flat and water sat against window

Back of niche has no waterproof and is tiled directly on the inside of the next rooms drywall

I plan to redo with Kerdi board

After I remediate the bit of mold, any tips for the insulation and maybe Vapor barrier I should be using that again??

There was some slight dampness against outer walls and top left corner of this wall