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).

The Lee Oskar and the Hohner Special 20 are probably the best good harmonicas for a beginner. The Marine Band is more iconic and the Blues Harp (not to be confused with the cheap Blues Harp) are in the same price range and good harps but they have wooden combs and can be rough on your lips when you are starting out.

Yes, but you can speed up the process a lot by learning from others. There are many great harmonica tutorials on youtube, for example. Different teachers work on different styles of playing and different genres of music, but the most common is blues harmonica.