florinc,
I really like the breakaway idea for lateral boards (Elevators). Someone at a tradeshow also only wanted 2 slots and I said to him that nothing really prevented you from taking a dremel to it and making it the right size and # of slots for your needs.
Grumpy_Mike,
Let me clear up the different Tower modules you see for sale.
TWR-MCF51CN-KIT = complete kit with 2 Elevators, 1 MCF51CN MCU module, 1 Serial module, plus quick start guide, labs, etc.
All the components sold in the KIT can be purchased separately and that is the other 3 options you see that are less expensive. You have:
TWR-ELEV = lateral Elevator modules that interconnect the modules
TWR-SER = serial module that includes Ethernet, USB, CAN, and RS232/485 circuitry
TWR-MCF51CN = MCU module with basic components for standalone operation, programmer and MCF51CN ColdFire V1 microcontroller.
Another good reference for the Tower System is Tower System Modular Development Board Platform | NXP Semiconductors