I've started a job as mobile lead in a 100employee company. Their Mobile products (iOS and Android) has been developed by external teams, and now they have decided to assemble internal teams, so I'm heavily involved in hiring ATM, both for iOS and Android. I will have teams of 5 people for each of the platforms. I've been manager before, but it's the first time I'm not starting code from scratch.
My question is how to handle taking over code? The iOS code is about 50 classes, many of them over 700 lines. The code quality is around 5/10. What should be my first steps for taking over the code base? Little by little or major restructure first, or both using different resources?