In Mist, there are some addresses listed as accounts, and some listed as wallets. What's the difference? Which should I use? And why do I need Ether to create a Wallet?
Accounts are the most basic way to store Ether. They are simple public/private keypairs, which you use to sign transactions. You don't need to do anything to "register" an account with the network, just generate one and send some ether to it.
Wallets are smart-contracts that allow for advanced features such as transaction logging, multisig, withdrawal limits, and more. In order to create a wallet, you need to deploy the contract to the blockchain, which requires ether. You need to make sure you keep track not only of the keys required to access the wallet, but also the wallet address. Unlike with accounts, wallet addresses are not very easily derivable from the private key (although it's not the end of the world if you lose the wallet address, you can use a block explorer to find what contracts you've created recently). Technically you can recover the address from just the account that created it and the nonce of the transaction, but that's a hassle.
tl;dr: Start with an account, get some Ether, then create a wallet and store your ETH there