You can try to use it the way you propose , but be aware:
-RTC may not be used (I haven’t tried…) but time synchronization it is slow…
-all pins 8+3 need to be declared on pins.h file and ESP8266 has no sufficient GPIO
-you may try to give the pins you are not using a dummy number but must be an available GPIO.
-3 pins are necessary for OS buttons.
Much better to use an expansion cip: or a PCF8574 or a shift register cip.