dont store all your BTC all in the same way, with the same website etc. when there is one mistake, you lose all.split your funds. you can use:
1. hardware wallets
https://bitcointalk.org/index.php?topic=899253.02. paper wallets
3. Xapo.com
buy a good antivirus and maleware programm.
Heed this advice.
Indeed.
Also, personally, I wouldn't feel safe having a large amount of coins in an unencrypted wallet. I would just connect a clean computer to the internet for a minute to encrypt the wallet. If someone ever accidentally gets the same private key somehow, it is still safe.