Basically, it's all about their performance through their gains and losses and the metrics depend if it's on a 24-hour trade basis or if it's a week. But AFAIK, it's gotta be both of them which can be set by anyone who's looking for the top-performing traders.
and how do these platforms handle risk management for traders and investors?
It should be the users that should handle risk management and not the platform itself.
Do they offer tools like stop-loss orders, margin requirements, or position limits?
Most likely with these platforms like copy trading platforms and others that have been mentioned on the article, yes, they do offer stop loss and for you to know more about them, you should start using any of them.