Narrow plot with boundary construction - Various questions / problems

Are you allowed to install roof windows on the sides?

Google "shortgun House plan"
They are also long and narrow. Although sometimes with windows on the sides, but not always.
Have you ever checked out [schöner Wohnen]?

For that plot of land, you need an architect who can do more than just a city villa.

Honestly: I don't see a big problem with the floor plan.

EG: front left kitchen, front right hallway, cloakroom, WC, back: living room
OG: one room in each of the four corners, hallway in the middle, stairs, storage room, windowless bathroom

I would look for an architect who has experience with building gaps

For this plot of land, you need an architect who can do more than just town villas

I haven't heard from in a while, I would consider him suitable. Which area in RP is it about? If I remember correctly, he was located in Bad Münstereifel.