How to render and plaster a portion of internal brick wall?

[dsyabb]

Hi, I knocked down a small brick pony wall and now I need to render and plaster. What products will I need to get and what is the easiest way to fix it so it is flush with the existing wall? I know I need to fill up the gap in the wall first too, but not sure what I could use. The flooring will be replaced so it won’t be an issue.