Mostly, but not completely. The hog & gunwhales are solid timber and run the length of the boat; there are other smaller bits.
Yep. Usually the wood breaks (gunwhales) and has to be replaced in that section. I've never seen the joint fail; it seems to be tougher than the wood.
They're too stiff to bend much. The major construction units are a pair of foot-wide box sections.
The loads on the boat are a lot higher. Some types run several tons of tension in the rigging and that's on a hull of ~100Kg.
Mostly I've seen wood moving because of water - humidity changes etc. We epoxy coat the whole thing - keeping them dry keeps the weight down.
Andy