Do not hold your coins in a exchange . If you were following the social media you could see that at least 2-3 big exchanges are getting hacked each year and millions of usd are lost . You should buy a hardware for holding your coins safe
Big but not top-5. I think if one of them is hacked, the whole market will collapse.
Keeping coins on the exchange is not bad if you trade constantly, otherwise it’s really wiser to use some cold wallet.