How to deal with this window reveal and insulate?

[Sensors]

I've recently had new double glazed uPVC windows installed, and since the old sash and case windows were so rotten they stripped out the whole frame with the rest of the windows.

The old lime plaster on this wall basically fell off on its own after decades of damp/neglect by the previous owners, so I've stripped it back to brick and plan to insulate this wall with 75mm PIR bonded with adhesive foam, and then plasterboard bonded onto this. I can see into the draughty wall cavity at each side, so I'd like to inslate the window reveal too.

From PVC edge to wall I have around 10cm at all sides, but I'm not sure what I need to do to insulate this. In terms of order, I'm guessing I should create the window reveal first so I can align the wall insulation?

Any advice appreciated!

 

[Mr Chibs]

When I've done this type of thing before I've wedged the left and right sides in situ (leaving a 10mm gap to the reveal) and over a few applications, filled this gap behind with expanding foam. Then I cut a section out of the side insulation sections and slide the top bit of insulation, (the notches hold it in place) again back fill if needed.

I just stick the bottom piece in with foam.