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, metamask is only work for ethereum network. You can store ETH or all erc20 tokens on it.
I have using metamask since it created. So far it is good using it, you dont need to input your private key to doing any transaction in your eth wallet.