Makes lots of sense. What if my offline device gets broken, or burnt, or w/e? Is there a super safe way to store bitcoins? I'm getting to the idea there is no 100% safe way to do it. My online wallet could get hacked and my offline USB/HD could crack...
OS does matter to be honest . Using Linux would be better then using Windows because most of viruses out there are written for Windows.
So you could increase your safety by using Linux .
I would suggest you to use Electrum as a wallet , because It gives you a 12 words seed when you setup the wallet for the first time , and you can recover your Bitcoins & wallet with those words in a case of a computer failure or device get burnt as you said etc ... So just keep those words in a vault in a piece of paper or whatever . and you should be fine
~ Madness