It is risky but you can certain small amount kept on exchanges.
Why is that good? You can react fast if dump occurs or wait for alts to wake up like Dogecoin recently
Just dont get goxxed. Only keep on the exchange what you would use for trading. If you dont controll the private key, they are not your coins, but a mere promise from someone you probably dont even know.
Yes its is risky but how to trade without exchanges?
All those manipulations can increase your holding at the end.. Why not take advantage of that?
There are wallets as Xapo, that allow you to convert your bitcoins to FIAT rigth away, however the fund will stay on that wallet, if you need to withdrawl it , then you need to convert to BTC again, and send it to some external exchanges .