No, the distances between the shelves are fixed. You push the elements into pre-milled slots (4 cm) in the back bar.
2. I can't say, but why bend them? The shelves give a little with the weight of the books, but they fit well.
3. the assembly is not complicated, I threw it away. The back bar is 5 cm wide and 5 cm deep. It has a hole at the top and bottom (each 10 cm from the edge) for hanging screws. I can't tell you the size, but you can work it out with the weight of the books.