Today i spent about 1 hr learning a bit more on using the zremesher tool for face topology in ZBrush.
Here's a video i made starting with result from the hour and going backwards. The main take aways were that it felt like zremesher liked smooth faces to follow guides, and also i think it likes to work on as a low res as can get away with holding shape. And another take away if wanted default mesh lips closed can still model it open in ZBrush then use joint weighting in Maya to close middle of lip then can use ZBrush to tweak mesh.
Hope you find this helpful.