A bomb seems the most plausible explanation, but that would produce a massive debris field on the ocean.
Yes, but small enough to make it hard to detect for visual searches. Large pieces could certainly be found quicker.
If the plane exploded in 35'000 ft then the mass of debris would spread in a very large area. And remember Af447. The pieces were found, if I recall right my memory, more than 100 miles off the position where they were thinking of what Af447 position must have been. The debris drifted with the current.