I only use Linux for sending coins, or storing wallets.  I have backups of wallets in multiple location on multiple USB drives.  On those devices i also have the public/private keys.  The linux laptop I use for coins is off at all times, and the wi-fi is only enabled to update the blockchain (when needed).

I never keep coins or USD in an exchange for more than a few hours (send coins in, convert to other coins, or sometimes sell a decline and buy back lower).

The wallets I use to send mined coins are on Windows machines - and they are only used to receive coins from mining activities, then immediately send to the offline wallet stored on the laptop etc.