I would just use the free Instant Meshes retopo software, it's the same algorithm that Modo uses and gives comparable results to Zbrush's ZRemesher with organically shaped models. I've used both and for general auto retopology they're pretty similar really, for your purposes it will be fine. If you're uncertain just do a little research, can't beat free and a good reputation.

https://github.com/wjakob/instant-meshes