There are two block explorers live today. You can find them here:
Once you complete a successful staking or delegation request, your tokens are sent to the staking contract. Your tokens are not lost - they are staked! To view your active stake or delegation, navigate to the Stake & Delegate page on Flow Port (left side bar, or this URL + your address after the last slash (https://port.onflow.org/stake-delegate/)
Yes, accounts support multiple, weighted keys, here
fun addPublicKey(_ publicKey: [UInt8])and
fun removePublicKey(_ index: Int) functions.
Accounts are created with associated keys. There can be multiple keys on an account. To execute transactions from the account, a total of 1000 weight keys need to sign. The account holds a field for FLOW balance. When transactions move flow, that balance is updated by the protocol. The account also holds place for storage and contract code.
FLOW supports a variety of signature schemes for adding keys to an account.
Instructions to generate an address are here: https://docs.onflow.org/flow-go-sdk/creating-accounts. You don't need a service account.