to build a new wall onto an old wall

Two and a half square meters of wall will be newly added from the outside to our house. I am considering doing it myself, but I have an unresolved technical question about it: The old wall is plastered. To connect the new one with the old wall, I will insert reinforcing steel bars into a few joints. A foundation for the new wall sections is present. Is it sensible to remove the old plaster beforehand, or does it not matter?

Oh, the narrow side is adjacent to the house, not the large surface ... these will be two 50 cm deep side walls for an extension of the house entrance.

You all probably want the extended front entrance above me to collapse?

Isn't there a mason here who can tell me something about that?
(no, the matter is probably not that important, but since I'm doing the masonry myself, I want to get such details "right")

What should the new wall look like? Also plastered?

I would leave the old plaster on to protect the building. Then set the new wall about 1 cm away from the house with a movement joint, and then close the gap, for example, with color-matched silicone.

Yes, plastered, basically like the existing house.

Movement joint? The space between the walls will be connected to the hallway, or rather extended (by 50 cm). A joint doesn’t make sense to me there (especially since the two short wall sections would then be standing completely free). But that’s exactly why I’m asking. Most of the time, the answers include completely different aspects that I hadn’t thought of before...