Is the seed phrase 12 words?
Yes. The seed phrase includes 12 words. If you have it, there's nothing to worry about. It's enough for recovering your wallet.
In the case the new OS doesn't support electrum, you can import the seed phrase on another device and access your fund.
When you say back it up, do you mean onto an external hard drive? Sorry for the basic questions, I'm not tech savvy at all.
Keep the wallet file.
It can be on an external hard drive or any other place.
Can you confirm I can recover my wallet with the seed phrase even if I can't get electrum to work on the computer that the wallet was sitting on?
If you have the seed phrase, you can recover your wallet using electrum on any device.
If your wallet has been funded, you can use
bluewallet too.