Hi,
the smallest amount of memory we can erase is a block. See the Table 5-4 on page 166 in RM:
http://www.nxp.com/files/32bit/doc/ref_manual/MPC5744PRM.pdf
The size varies from 16KB to 256KB.
The smallest amount of memory we can program is one double-word (64 bits). That's because the ECC is handled on 64bit boundary. Read the chapter "32.4.1.2 Program" in RM for more details.
Read-while-write is supported between partitions. Once one partition is being modified (erase or program operation is executed), we can access other partitions.
If you use EEPROM Emulation drivers (http://www.nxp.com/files/run_time_software/device_driver/MPC5xxx_EEE_DRIVER.exe) then, as you know, you can select fixed or variable length record scheme and you can select the size of records in bytes as needed and the drivers manage everything internally.
Regards,
Lukas