Please find our comments for the questions.
1) I2C connection is provided to change configuration settings on the fly if required in the application. If only a single configuration will do then I2C is not required. It is just an option and not necessity.
2) You can connect them to GND
3) tLock parameter is related to startup of the device with the initial configuration programmed into the device. For any changes done to the configuration by I2C you can refer to table 20 in the datasheet. Within 1 ms you will observe the modifications made in the output.