Two points here:

Though I have never used expo on my models, I have tasted it on the sim. It makes your model react softer as Andy described. I means, if set up correctly, your model will not move in a snap if you put in a lot of movement on the stick. This I am told helps out in models that have the tendency to snap such as wing tip stall or stall with too much elevator. I found that on the 3D models in the sim, expo added a certain lag and slowed down how quickly I corrected in a maneuver eg a hover. Personally, I have never used expo, but then again, I have never used a model that requires it. Most of my models have 3D tendencies and very good low speed handling.

I think you are referring to radio interference. Obviously, in the fixed frequency radios, two people on the same frequency cannot fly together. Solution to that is to go and check with everyone as to what frequency they are flying and locate next to each other on the flight line if you are so you can keep an eye on each other. Alternatively, if you go to 2.4Ghz setup, there is less likelyhood of interference. However, the way to avoid interference we found is to check clear frequencies and not fly with more than 5 airplanes at a time in the sky

Ameyam