balancing old cases with agile practices

Question

My team is just getting started integrating agile practices (we've chosen kanban) into our dev, test and design teams, but we have a lot of bug cases and feature cases not written in user stories left over from the old system and we're trying to find a good way to take care of the bugs but still keep the devs that need to stay heads down focused. for now we have a newer dev assigned to bug fixes so the rest can work on new features but we are looking for the right way to structure the team. We have 7 devs, 2 testers and 2 designers.

Thanks in advance for the help :)