1) generally, dialogue and banter works well for creating funny scenarios. Embarrassing a character can also create humour. Fluff depends on how well you've developed your characters and how believable their relationships are.

2) making a character relatable to the reader is generally a good way to tug at a reader's heart. The closer a reader can get to empathy - understanding and relating to what the character is going through - the easier it is for a reader to become attached to them.

3) I don't think you should ever aim for a certain amount of chapters, but if you do, always make sure you have some idea of the beginning, the middle, and how it ends. If you have things you need to cover, make sure you know roughly where those parts should be. It makes it easier to have filler chapters between important events, and gives you something to work towards.

4) I didn't realise you were a writer. ^^

5) There's no outright cure. Everyone deals with it their own way. I like to write oneshots different from what I'm working on if I am stuck on a multi chapter fic. Sometimes listening to music helps. Sometimes watching YouTube clips of the actors/singers I'm writing about will give me ideas too. Other times, I'll just talk to people and usually we'll talk about our biases or OTPs, and something will inspire me from that. Everyone is different though. :)