How to insulate window reveal + cavity closer

Hi guys

I've removed the plasterboard, window board, adhesive etc from my garage window reveal (this will be done to all my windows but using the garage as a test).

The garage (on side of house and has an internal door to my utlity room) window reveal has no cavity closers, I do know most if not all my house window reveals do have them though.

For this reveal should I get some cavity closers or use pir board and foam the board into place. I was planning to do the following:

If I use pir board should I get the right thickness for the cavity and have the reflective backing so it faces the outer brick and the inner block or get whatever thickness I want and cut the right thickness and have the reflective lining facing me as I fit it or does it matter? I can do this on the left, right and under the window board. 

I was then going to get 12mm (maybe even 24mm) pir board and line the reveals completely across the blockwork over the cavity closers or make shift cavity closers, under the window board and covering the lintel. 

Should I use normal expanding foam as an adhesive or buy some actual foam adhesive for this part of the task?

I plan to get a joiner to make up some birch ply linings for the reveals as I like the ply edge which will face into the room for a contemporary look and paint the reveal linings, these will be mechanically fixed into the block work, I'd like to foam/glue them in but not sure how to make them stay in place and solid but we will see.

Before all the insulation is added, the gaps between windows and brick work will be foamed and I planned to tape up over the this too. Yes it may unnecessary but I'm going to do this properly. If I use tape should I tape between window and cavity closer or tape before adding the closers in?

I will be adding new cavity batts where they are missing (you can see this in the pics below). I will also foam the gaps where the existing plasterboard has been dot/dabbed.

Pictures are below of current garage reveal

thanks James