One block contains 1MB of data. There might be up to 4000 transactions in one block.

Recent transactions are included in a block. Bitcoins are generated with the creation of every block.

Wallets involve cryptographic keys. Your private key is the thing to keep secret.

Smaller networks are more vulnerable to attack.

"Reliability of the network generally depends on how actively a blockchain network is monitored and maintained, as well as the financial incentives for operatingthenetwork" ("Blockstack: AGlobalNamingandStorageSystemSecuredbyBlockchain")