New drywall flush with brick wall

[PanGad]

Hi All,
Together with my partner, we bought a house that needs some reno. It’s a cross wall construction 60’s house. We want to do as much improvements ourselves, however we have only limited experience with building work/ DIY so some help and advice would be much appreciated. I am new to the Forum so sorry if this topic/ matter has already been discussed. I tried searching but after a while of no success I thought it would be better to give it a go with a new topic. Here we go:

At the front and back of the house, the walls are constructed as timber frame with hanging tiles. They didn’t seem to perform thermally and have cracks where they meet the brick side walls so we wanted to look into it. They only had a very thin polystyrene with a reflective surface as insulation behind the plasterboard. Under the hanging tiles there is felt. We are planning to replace it with a breather membrane in due course. We also discovered (I mean it’s clear as day) that the walls are not plumb.
To improve thermal properties, we want to fill the voids between existing studwork with insulation (we are keen on Actis Hybris product), install a new studded frame in front of the old one that will be plumb and cover it with a multifoil insulation (ie with vapour barrier) and plasterboard.
At the front and back of the house, the side walls (that are concrete block) are finished with brick pillars that are wider than the walls, creating projections into the rooms. Dims vary but roughly 100x100 mm - see attached photos.

When building those newly insulated walls, we want them to be finished flush with those projections. We will also need a new and longer window sill to cover it up.
I am wondering how to make the joint between the drywall and the brick pillars to avoid cracking. Tape it first and plaster over?
How would you approach this job anyway? Perhaps I am overthinking it?

[wine~o]

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