What to do with chunks of missing plaster

In the process of refinishing the floor in my office, I took the original trim off the wall - unsuccessfully I may add :’), and now I have chunks of plaster missing. Any recommendations on best thing to do moving forward? Also, I live in the Midwest and the winters are cold. I can feel every bit of outside air in the gaps. When I shine a light in, I don’t see any insulation. Is this as good of time as any to spray in insulation before repairing? Very new to all of this and the DIYing. Thanks in advance.