External wall preparation

Hello, I'm about to get my basement lined out with an internal wall. This will be a timber frame baton wall with 3 layers of 15mm drywall. I may substitute the 1st layer for plywood as recommended on this forum, to provide better structural integrity and easier fixing once the room is finished. There will be a 100-200mm void behind this internal wall filled with 100mm dense rockwool. One of the external walls has a gap at the top before the joists for the room above start. See diagram.As you can see most of this wall has earth/soil behind it so sound isn't going anywhere. The room above is the kitchen. It's floor span includes the basement and another section which you can see to the right of this diagram. It is a normal suspended timber floor. What I'm wondering is should I build this wall up to just below the timber floor and fill the gap with rockwool or is dot n dabbing some drywall to the top of the wall and filling any gaps with rockwool enough. In someways this is no different than the ceiling above my structure so maybe not a weak point? The other thing I'm considering here is ventilation to the subfloor timbers and joists above my structure. Although my basement has been tanked and is no longer showing any water or damp there will be condensation in the void between my external wall and internal wall (tanking always "sweats" a little) and this needs airflow to prevent any timber problems over the years. In a normal construction I'd just pop some airbricks above the DPC in the external wall but that would obviously compromise the sound isolation. What's the best way of getting good airflow to this void? (The main room will have AC but that wont help the void behind this internal wall). Thanks in advance for any help :) Chris