I'm a newbie with some technical skills, but not a lot.
Should I be using MetaMask for added security?
What does MetaMask do for me, exactly?
Also, MetaMask seems to only work for Ethereum-based coins. Is there an extension like MetaMask available for the other coins?
Yes, of course you can use it. You can also sync or connect it to your MEW account. It is secure, but if you like more security I prefer using a hard wallet like trezor or ledger.