So connecting two controllers is possible using the serial connection. But this project has continued to grow since I started it 13 months ago and sooner or later I will want 3 controllers either due to memory constraints or the need for more sensor/motor inputs/outputs. Will it be possible for me to interface 3 controllers in the future or is 2 controllers the limit for VEX and I need to look into other options?
Yes, you can connect more than 2 Vex Controllers together. You have 2 Serial Ports on each Vex Controller: the Programming Port and the TX/RX pins. You would have to connect the Controllers together in series. Controller 1 could talk to 2 other Controllers A and B via the different 2 Serial Ports. The 2 new Controllers A and B could only talk to each other via Controller 1.