Many old mid century homes had wall ovens installed into walls, so, maybe. You give zero measurements, or anything yseful to determine if it is possible. But that is probably a load bearing wall that would need it’s weight bearing redone.

I am going to say probably yes. But the framing may be a little tricky, load bearing or no. If it is I think it would be like putting a window in a load bearing wall, the span is not large typically ovens are 30. You will have to watch headroom.

Frank Lloyd Wright has a grand piano hanging out over the back stairs of his house. I think if you are tall you might have to duck.

Would you be removing the handrail? How will this work with the stairwell there?

I think the plan is to cantilever it more or less into the recessed area above the area where the light fixture is. Like the bottom of it would be around the bottom of the fixture.