It depends if it's an interior door, or the front door. If an interior door, if you wall it off, it looks like you might obstruct part of the door frame. I don't know if the other posters are talking about walling it off in a "box," or creating an entire fake wall across that wall, which which case you would need to either move the baseboards, or get new baseboards - and those are old baseboards and you may have to have them custom made - even though they are not fancy baseboards. As an alternative you could repair the holes in the floor and ceiling and paint the pipes the same color as the walls. A good drywaller should be able to repair the open ceiling corner. If you wall it off in a box shape, it could have the potential to look cheesy. In my previous house, it was an old house like yours and had the furnace pipe running up from the basement through a corner of the bathroom through the roof. I painted it the same color as the wall and it looked fine. May be difficult to get in the corners behind the pipes, but it's doable.

Just Google "Wall Stickers for Boy's Nursery" A million photos will come up. Consider the decals as a teaching moment for the boy. He could be able to identify animals or recognize his name.

Your dining room table and chairs are classic and will never go out of style. Your rug too is great but I would move it to another room and replace with something much lighter in colour, perhaps another oriental rug or maybe something more modern. The spaces around your dining room have wainscotting with panels below. Those bottom panels are missing from your dining room so I'd add them, the chair rail looks odd without the panels below. Then I would paint the wainscot the same white as the other wainscot. Paint above the wainscott a soft cream so it will be slightly different from the wainscot. On your window wall, move the plant to another room and add white linen drapes. Remove the tapestry, candle sconces, mirror, and that little table with the lamp (that table is much too small scale for this room, looks like baby furniture). Add a single piece of art to the tapestry wall in large scale, don't do small pieces. Replace your chandelier with something more current and reupholster your chair seats in solid cream (this is an easy DIY). And then stop. Your dining room table and chairs are the stars of this room. Keep it simple. Table, chairs, rug, drapes, chandelier, one large piece of art. And BTW, your table looks really stately with the extensions, I'd leave them in all the time. Perhaps one more decor item would be something for the middle of the table. And make it one single thing and make it large scale.

Hang the painting centered 5' above the floor on the wall opposite the window. Replace the brass light with a larger one that has some French flair and hang a mirror to reflect/double it. It should hang about 32" above the table. I would upgrade the lights in the foyer/stairwell too. Those seem very 1980's in style. Drapes would be a plus, as would a rug under the table. A sideboard would look good under the painting/bulkhead. Then lower the painting to 5" above it.