firmware have a 96 buttons + 10 axis
possible to use for joystick: 64 buttons + 2 hats(8 buttons) + 8 axis
possible to use for mouse emulation: 3 buttons + 2 axis
possible to use for keyboard emulation: 12 buttons (or 15 without "mouse")

if you want to take more and use less pins of you MCU:
for axis - MCP3208, 8 channel 12 bit ADC (minus 4 pins, plus 8 analog axis sources)
for buttons - shift register 74HC165 or 4021B (minus 3 pins, plus UNLIMIT button sources)