Can I use statistics or made-up research in Task 2? Can I write "on the other hand" in an opinion essay? How many paragraphs?

Nobody fact-checks you, but made-up stats look like filler. A quick hypothetical example ("if a city banned cars...") works way better imo. "On the other hand", I think is totally fine, as long as your opinion stays clear throughout. Mention the other side, then shut it down. Just don't overdo the linkers.