The ATtiny family works with the same frequencies as the ATmega family of microcontrollers.
You're absolutely right! Actually I'd like to develop a bit banged I2C slave driver (hardware independant) to use it on a processor that have a higher frequency than 500 MHz. I haven't defined that processor yet.
you'll only find code that shows you how to use the hardware features you will need.
Yes that's what I need 
I never worked on a microcontroller before so developping a driver seems tough to me..
Thanks I'll re-check your previous answers