The second look like they are designed for stairwells so I'd be a bit wary about using them up higher as the light might be a bit "spotlight" and not diffuse enough. I think both styles work with your house design

Do this yourself it will save money. Figure out how much of the wall you are wanting to cover, figure out how wide u want the slats and then the gap. Then make sure you have the tools and order the materials from a hardware store or bunnings. Tools youll need are nails, hammer or brad nailer, level, pencil a set square. Thats all i can think of right now.

As in our house because the wall at the end of the passage was only a doorway space from the Arch there wasn't any load bearing problem Check with council to see if you can find any old plans, the Archway to the bathroom could be just because you could or that space had a different use a lot of bathrooms and kitchens were at the rear of house the house during that period

Looks beautiful. The pendant lights provide some balance for the open shelving, which being open with no upright against window add to spaciousness of window. By contrast your design is boxing in the window