ok I know what it was now, had a mirror modifier which was turned off for viewport, but not for render. simple really but these thigns can cause me hours of annoyance :)
Added normal dishes, modified the fabric signs that are hanging from the awning so they are different from each other, added stools just for the sake of it, added beverage cartons.
You could combine the two walls/windows into one asset that has seamless UVs. Or modify the design of the wall and incorporate something to hide the seam. A column, a pipe, etc.
Use the xForm modifier and collapse. Also if you don't like the white bounding box you can turn it off by unchecking "Selection Brackets" in your Viewport Configuration.
Hmmm, you could probably use something like the skin wrap modifier (taking the animation from the original mesh. There's probably a more efficent way of doing it though.