questions on data block size?

[David Huang]

Hi there,   I need to use the AES symmetric algorithm, RSA algorithm to encrypt  large data string or file, like 300k, or 1M. right now, I have finished the AES( CBCPaddedEncryptor/CBCPaddedDecryptor) and RSA(RSAES_PKCS1v15) algorithms development, but can only encrypt limlited length of data. So, I need to devide those large "string" into blocks. but I do not know how to determine the sizes of blocks. for example, we use RSA to encrypt data, if the key size is 512, what block size I should to choose?, if key size is 2048, what another block size I should choose? is there any equations in this library that I can calculate it?   for the AES CBC block cipher, should we keep the "iv" and "key" the same?   thanks     David