You can be trying as many as like, but one thing I would like you to know is that you should never leave all your coins stored in exchanges cause they can get hacked and you will lose everything. Most of these exchanges are vulnerable to hackers attack, so always have your coins stored in a safe wallet and backed up with keys so you don’t lose them. And don’t forget to save your keys where it will be safe. As for exchanges you can use for trading, I think Binance and Bitfinex would be good better options.