If it is to look like in the picture (it looks very nice), then there won't be much load to speak of, it can at most involve the load from 1m2 of sloped roof that the beam has to take.
I built something similar, my post is mounted in wood siding, with 3 8mm screws going into the frame behind.
The binding joist/top rail is then attached to the post.
Can you/can't you place the post on the "floor"?
Yes, it should be like in the image above. In option 2, however, with an additional post immediately to the right of the stairs. I can't take credit for the sketch, we hired an architect for a few hours several years ago.
Inside by the wall, there will eventually be a post, but not at the beginning since the house is to be re-plastered. The idea is, therefore, to attach the beam in existing holes in the wall and mount the (half-)posts against the wall later after the plastering.
The image below shows the not-so-beautiful reality with traces of the previous masonry porch that I've demolished. It would have been logical to re-plaster the house first, but it's a future project, and the new door needs to be protected as soon as possible since it is starting to show signs of weathering.
Regarding the beam, I'm a little worried that it will sag if I don't put an extra post to the right of the stairs, but you don't think there's any risk?
