I'd say one of the biggest stumbling blocks would be agonising over the data model / workflow. I predict this will take a long time and involve many arguments about what should happen to a bug under certain circumstances, what really constitutes a bug, etc. Rather than spend months arguing to-and-fro, if you were to just roll out a pre-built system, most people will learn how to use it and make the best of it, no matter what decisions are already fixed. Choose something open-source, and you can always tweak it later if need be - that will be much quicker than rolling your own from scratch.
