The main difference is that manga volumes usually collect several single chapters together. Volumes often have a coherent theme or story arc within them.
It depends. If you're a big manga fan and love having a collection, they can be totally worth it. You get multiple volumes in one go and can enjoy the series without having to hunt for individual issues.
First, plan your layout. Consider the theme and mood of the scene. Use reference images and learn different drawing techniques for textures and backgrounds. With time and effort, you'll improve.
It's possible for manga box sets to be fake. Sometimes, poor-quality reproductions are made and sold as the real thing. This can be difficult to spot for the average buyer.
Manga box sets are expensive because they include multiple volumes in one package. This saves you from buying each volume separately, but the combined cost along with packaging and distribution expenses adds up.