A 5 gallon carboy IS a wise investment. Many beers benefit from a secondary, in which you rack your brew off the primary yeast, and let bulk age and clarify. Having multiple carboys is beneficial as you will undoubtedly want to brew more than one beer at a time. I have 4 sets of 5and 6 gallon carboys for this purpose. The more the marrier!!! It seems expensive at first, but it is an essential investment in my opinion.