first you have a misconception, BTCs are only stored in the blockchain, wallet.dat stores public/private keypairs of your addresses, addresses can have or not BTCs to spent but that's irrelevant for the storage.

1. Bitcoin has nothing like a API for backups, but it does have encrypted wallets so you can encrypt your wallet file and you only will be able to use it if you remember the passphrase.
2. Having your wallet.dat file in several computers and actively using it in several pcs can cause address loss (and BTC in those addresses) see: If I backup my wallet.dat once, am I forever safe?
3. If the wallet.dat file stored in external sites is not ciphered and someone has access to it, yes that entity wil be able to "steal" all current and future coins on that addresses.