Will I need to purchase all new cables?

Not necessarily. USB 3.1 is backwards compatible with USB 2.0 and during the transition period most devices will include both Type-C and legacy Type-A connections, so you're still be able to use your current cables. Adapters are available now, which allow you to plug your legacy devices into a Type-C port, and hybrid cables with a Type-A connector on one end and Type-C on the other are also available, so as devices transition to offering only Type-C ports, you'll still be able to use your old cables.