For 1 2 and 3 we rely on the courts. It's already their job to decide when somebody has broken the law or not. The courts need to decide if a reasonable person could tell if some writing is sarcasm or fiction, and if it was written to intentional mislead, then its a crime. 4 is just a hard problem we need to work through.

5. The problem that needs fixing is that people don't trust anything they read any more. Nobody knows what to believe and can't make a good judgement call about what is a trustworthy news source. This results in a polarised, ignorant society.

If you post online that Trump likes your mums cooking, nobody is going to take you to court because the damages done is almost nothing. If you post online that Trump wants to evict all Chinese nationals from the country, well that's a lie that could cause some real strife, and I would be happy if that was just not written on the internet.