AVR-Chat

Hi again, I am seeking some info regarding linking multiple AVR modules together. In the design, there would be say a few Uc' units, each having their respective control circuits and all that stuff. I need to find out how to get each unit to be able monitor and communicate with each other module, and change states based upon the results of polling eachothers various inputs. 
 
 Eg. three modules each having a uC, stepper motor control circuitry and input sensors, such as push-buttons and IR rangers. I am trying to use the tiny45 for each uC, but am not sure if I am going to be able to do all needed functions using such small pin counts, but another problem...Anyways, say I wanted to monitor the states of each modules input sensors and drive each stepper in different duty cycles based upon the results of the inputs. The design is meant to be modular, and able to accept in theory as many or as few modules as needed in specific app. So they have to be able to work together and seperatly based on what is desired without much modification to hardware.
 
 Questions,1- if I need around four pins to drive the stepper on each uC, say one for the input sensors, and ? for uC to uC communication, am I going to have to use a different device, or can this be done using inturrupts or some other fashion?
 2- minimally how few pins can I get away with using for the uC to uC communications? for programming how would I approach the interface? ISP for each or able to program each device at same times, or both?
 
 Lastly, if I need 12V and 5V regulators, can I run the 5 directly from the output of the 12, and have no problems with noise or nasties like that using the outputs to drive (5 for digital and 12 for analog drive??).
 
 Well, thats it for now, and thanks in advance for any help with these! jaydag71- sunny Vic BC.
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