Letterbox and house identification number

I've decided to add an extra brick pillar on the left of the front path thanks to my lovely friends over at the Decorating Forum. It will mean removing the middle structural metal rod (?) and adding two to the existing fence footings. I am not even sure if this is possible or how difficult it is. Do you think it is worth the effort in order to add an additional post?

What I also wanted to ask you is, about the fence in between the front path and the driveway. Should we have it as a solid wall or two 350x350 brick pillars with a plinth in between? We will need a letterbox integrated into the fence, and the spot between the front path and the driveway seems perfect, so we can reach it from both entrances. Also, thanks to KL's suggestion we would like a house identification number close to the letterbox.

The fence length between the gate and the driveway is 1.12m.

Do you think having a solid wall would look too chunky? It would also hide the hedge on the right of the path ... What I am worried about with having two 350x350 posts is not having sufficient amount of space to incorporate a letterbox, and also the fact that we would have to choose between the driveway or gate post, and we won't be able to reach it from both entrances....

What do you think? Practicality over aesthetics?

B