Minecraft Backwards Compatibility

I believe they act the same as arrows;

They will fly in a parabola (arc) and will travel approximately 15 blocks when fired parallel to a flat plane. Arrows have a maximum range of around 50 blocks when fired at a 45 degree angle on a flat plane.

No, ruins and villages are generated with the world, not actively built. If that changes in a future update, then it might not be required then, but for now all new geographic features require you to generate new chunks.

The usual way of doing this is just making a new world with all new chunks, but if you walk to places that you haven't yet, then new chunks will generate. (Potentially with new features.) It's still recommended that you generate a new world though since you might have to walk a while to get to new parts, the boundary between versions might not line up right, and biomes might shift(especially with the addition of a new one), but if you haven't explored much or really like it so far, it might be worth it.