I have little knowledge on desktop wallets but as far as I know if I have the private key of my wallet stored somewhere safe and if someday my hard disk blows up, I can still get my wallet and full balance back with the private key, is that correct?
It is a little bit more complicated than that, but yes you are right. With electrum, rather than dealing directly with your private key, you have to
memorise a seed. Your seed is a random sequence of words that correspond to your private key. And you can write them on a piece of paper and store them securely. In case your hard drive blows up, you can install a new installation of electrum wallet on a new disk and just import your memorised seed and all your balance is under your control again.
Also can I password protect the electrum software?
Not that you can, but you
should. That brings another layer of protection to your wallet.