Thats right. Four ports will give u 32 pins. If this is still insufficient, two methods are common:
1) memory mapping of the I/O Devices. Use the 74138 type decoder with '373 latch for A/D bus and if required, some additional logic to map the devices. This way u can add many devices to the 16 bit address bus.

2) Use the PPI like 8255. u will get 3 additional ports. Alternatively u can use the PCF8574 (I2c bus I/o expander) which can be controlled over 2 I2C bus wires (2 port pins) to get the 8 I/O lines.

Regards....