Hohner is the oldest and most popular brand of diatonic harmonica. The Hohner Special 20 is probably the most common and best Hohner for beginners.

With regular deliberate practice, you can expect to be playing simple pop tunes within around 3 months. Within 6 to 12 months, your technique will improve and you will probably be able to work on bending notes (a very important skill for getting the best out of a harmonica).

There is no difference. A harmonica is a mouth organ. There is another instrument called a glass harmonica that is not a mouth organ, but a musical instrument consisting of a series of rotating glass bowls of differing sizes played by touching the dampened edges with a finger.