The maximum clock frequency of the MSP430F5359IZQWR is 25 MHz.
To configure the MSP430F5359IZQWR for low power consumption, use the low-power modes (LPM3, LPM4) and adjust the clock frequency, disable unused peripherals, and use the Power Management Module (PMM) to control the power modes.
Yes, the MSP430F5359IZQWR can be used with an external crystal oscillator. The device has an internal oscillator, but an external crystal oscillator can be used for more accurate clocking.
The MSP430F5359IZQWR can be programmed using the Texas Instruments Code Composer Studio (CCS) integrated development environment (IDE) or the IAR Embedded Workbench. The device can be programmed using the JTAG or Spy-Bi-Wire interfaces.