Hello again and thank you for your reply! I've just imported the wallet to Electrum.
You did not import your wallet into electrum.
You created a new electrum wallet and imported private keys from your core wallet.
Is it OK that there is no seed option? You can't click on the Seed option.
There is no seed option because you have imported private keys.
To use the option of a seed you have to create a new wallet and send your funds to your new wallet.
I already created a password and saved a copy to a couple of flash drives. So if I format my drive, I just have to open the file, insert password and I should be ready to go? Is there another way to protect everything?
Yes.
There are a lot more ways to protect your holdings.
You first have to know against what you want to be protected.
Is there anything else I should do or can I just delete Bitcoin Core? I could really use the space in my HDD.
You should create a new wallet and use the seed option. This makes backing up your coins way easier.
Transactoin fees can't go lower than they are nowadays.
If its only because of the space.. you can use prune mode. This way core does not store the whole blockchain.
If your backups are correct (you have tested them), you can safely remove core from your hard drive.