I want to make it clear I never ever needed an Electrum Desktop Bitcoin Wallet which I am using Windows 7 and I am told that it's the worse O.S. to use and Mac second safest and Linux being safest.
I have a Oracle VirtualBox VM [...]
Regarding safety overall, yes. That's correct.
But as bones261 already pointed out, in a targeted attack it doesn't matter which OS you are using.
Since 98%+ of all malware is written for windows, using MAC / linux is definitely a safer option. Especially when storing BTC on your computer.
Note, that running linux in a virtual machine won't protect you at all.
If you host (your win7) is compromised, your guest (VM) will be too. Just not vice versa .
Hardware wallets do not only store your private keys encrypted.
They have a secure element built in, which does not leak the private keys under any circumstances.
The secure element itself is responsible for signing transactions upon approving them on their built-in screen.
The private keys are basically always cut off from the internet or from an internet-connected device, which is not the case with your computer.
Encryption is only one (small) aspect which makes a hardware wallet secure.
Where electrum is installed doesn't matter.
It matters where your wallet file is stored.
You can easily install electrum directly on your main drive, but store the wallet file on your encrypted hard drive.
But generally, yes if your wallet file is stored on a drive which is connected to your computer all the time, it is less secure than a non-mounted and/or encrypted hard drive.
However, once your computer is compromised (e.g. with a malware which waits for you to open electrum), it doesn't matter where your file is stored if you open it anyway at some time.
You CAN use it wherever you want.
Make sure to have a backup of your 12 word mnemonic code, and you are fine.
Feel free to ask as many questions as you want. A lot of us will be happy to help you out where we can.