Method for measuring volume of gas I would like to setup something up my office to accurately measure the amount of Carbon Dioxide (CO2) being released from beans.

I looked at the site http://examples.yourdictionary.com/examples-of-ways-to-measure-volume.html which suggests several methods, the first of which, fluid displacement, I was going to employ. I know that CO2 is slightly soluble in water so I was going to use a saline solution/brine to reduce solubility. Can anyone help me here in explaining additional things that I should be doing to reduce errors in measurement with this fluid displacement method, other than of course reducing the possibility of air leaks and CO2 solubility? For example I have been reading about the risk of water evaporation in the measuring cylinder so I wonder how this can be minimised? I've also heard about the vander waals methodology for accuracy in calculation.

What other methods should I be considering? I'm not asking for better methods as I realise that's subjective, but other methods that you believe I should be investigating as possible alternatives. I have looked at a gas syringe and a balloon as alternatives.
Unless you have a way to separate CO2 from the rest of the gases, you won't be able to measure it properly. Which isn't easy. You could put a substance that absorbs carbon dioxide inside the container for the beans. However, the substance needs to be able to indicate that it has reached capacity. And also, the volume of CO2 that it can absorb must be known. 

You could also set up a respirometer. You could make some assumptions about how the oxygen is consumed. Nevertheless, it should give you a good estimate. There are several videos and tutorials explaining them. And if you still have questions, you can ask Bio Stack Exchange.

The comment about the van-der-Waals equations: I think that you were probably thinking on using the ideal gas law to estimate the number of gas molecules in a container. 
$$pV=nRT$$

According to the equation above, you can measure the number of particles if you know the pressure and the volume. This is true for ideal gases. For a gas molecule to behave like an ideal gas particle, it would have to have no volume and have no interactions with other gas molecules. Real gases, however, do not behave like an ideal gas.  Therefore, a better model to describe real gases is needed. The van-der-Waals equation is one of these attempts.