See you need to act smart if you are having lot of bitcoins,first do not store all of them at one place especially in online wallets,they are prone to hacked,use good paper wallet and save big amount of bitcoin there.secondly don't tell anyone about private keys of your wallet,don't save it online too,keep these things in mind and you are good to go.
Just get a hardware wallet weather it is a trezor or even ledger go and purchase anyone. Handling too many wallets is sometimes really hard and anyone mistake can be too costly for us. Storing in trezor ensures you don't can trust everything with just a single wallet.
Make sure noone has access to your private key, devide your holdings to different wallets (with different private keys) just for the case that one wallet get hacked one day. And store them in a secure place (e.g. paper wallet in a bank safe). Do not leave your holdings on a exchange.
Storing on exchanges is surely the biggest threat with the recent hack on bitfinex again we should really be cautious while using exchanges. What i would suggest you if you wanna trade use any exchanger like changelly it does require you to instal additional wallets and might he time consuming but it is way safer.