- A 128 bits key is expanded into 11 round keys of size 128 bits.
- A 192 bits key is expanded into 13 round keys of size 128 bits.
- A 256 bits key is expanded into 15 round keys of size 128 bits.
If you use a longer key, more round keys are produced, but they won't be longer. The security is increased through the number of rounds.
AES always works on 128 bit blocks. CBC mode means, that the 128 bit message block is first XORed with the 128 bit cipher block of the previous block and then AES encrypted.