The brain unit

Finally I have made up my mind! Excuse the pun, but it has been a painfully slow process deciding on the exact type of controller.
First, I had thought of an MC68HC1x, when budget grew tight, forcing me to consider recycling an old Sinclair ZX Spectrum, which was just available at that moment. When I was researching the possibilites of interfacing it to the outside world, I stumbled upon the AVR series of microcontrollers, which are cheap and versatile. So I stopped the already running PIO project in favor of an AVR.
Now the brain unit consists of an ATMEL 90S4433 "AVR" microcontroller, an 8 bit CPU with 4K flash ROM, 128 bytes SRAM and 256 bytes EEPROM. Of its 20 I/O lines, 6 are used for motor control, and another eight for sensor input. Three lines control LED indicator lights while the remaining three are dedicated to the programming interface.
Currently, I don't make any use of the AVR's analog/digital converter, but it is just fine to know it is there, should the need arise.
As it was really simple to design the circuit board and get it running, nothing should stand against integrating more controllers for specialized tasks. I might transfer the engine control to one or two engine controller AVRs, and sensor handling to another one. There could be controllers for output tasks (imagine speech output!), memory purposes (an environment map?), and many more.