I modified browian motion simulation to fit most of your request.
The following is 1000 particles randomly distributed (position, velocity and direction).
Number of three different particles are NA, NB and NC, there mass are ma,mb,mc
The temperature T define the average velocity: V[sub]avg[/sub] proportional to sqrt(T/m)
The dimension of volume (e.g. 10 liters) is meanless if you mean to simulate a real volume.
Because there are almost 10[sup]19[/sup] particles in 1 cm[sup]3[/sup].
Unless the colume is just used to calculate the pressure.
For the same reason, change the width/height of the container will not be able to represent real case.
There are limitation for the simulation: for example: in real world, most of the gas molecular moving with speed faster than speed of sound. And there are more than 10[sup]19[/sup] particles in 1 cm[sup]3[/sup]. if you want to visualize it. The particle can not move too fast on the screen.
The simulation has to be design in a proper way to show the effect. And for different purpose, it need to be designed differently.
Please write down the real problem you are studying and what kind of phenomena you are interested.
May be we can find out a better way to simulate it.
It might not be necessary to calculate the collision between particles, unless you want to study the energy transfer between particles.
It will be better if you can write down the physics model of the system.
The following is the simulation I have created for you!