Good questions. The first, about cleaning the harmonica. After a quick YT search myself I see there is a need for a video on this that is clear. All the videos I found either missed out parts of vital information or were going into talking about taking the reed plates off. Which is not a good idea for your first time opening a harmonica up! So, note to self.. do a video for you on this.
In the meantime, saliva is the main culprit, so:
1. Play the harmonica without titling your head toward the ground. This will reduce the amount of saliva going in the harmonica.
2. After playing, tap the holes of the harmonica firmly on a hankerchief (or your jeans :)) to knock out any loose saliva.
3. Store the harmonica in it’s case.
Doing those three things will keep your harp playing smoothly and greatly lessen the need to take the harmonica apart.
As for more beginners tunes to play, you are doing exactly what I had hoped. Starting to play by ear! Keep playing those german folk songs and any other tune that is in your head! You’ll find many, many tunes, can be picked out using the major scale alone. Just make sure to keep a good pucker in place and stop to practice the pucker if needs be. If you keep playing tunes, while ignoring a messy single hole technique you could introduce a bad habit, that is hard to break.
I hope that helps Felix, and If anyone else wants to jump in here with comments, be my guest!