It's certainely not something i would do with a F84. There's no ADC, no PWM module etc etc.

If it was for me, i would choose a better one, 16F88, 16F648,16f676, 16f684 etc etc.

But begin by understanding some part of your stuff first. You need to multiplex your displays (7 segments), see this one
http://www.picbasic.co.uk/forum/showthread.php?t=5297

Have a look in the PBP manual for ADCIN (what you need to read your ambient light) AND HPWM (what you need to play with your display brightness)

Try something, block by block... and then if there's anything that doesn't work, post your code and schematic here.

Have fun!