Zremesher would take forever on subdivided mesh like several mil one. And usually you never get it right from first attempt. Still it's a simple way to get even quads before subdividing. It does it slightly more clever than Dynamesh. So yeah > Import or free sculpt with sculptris and booleans in mid res >zremesh> export>…
if you need more geometry so that you can work at a higher resolution you can subdivide. if the flow of the geometry is making it difficult to sculpt the shapes that you want you can use zremesh or sculptris or dynamesh. Sculptris and dynamesh or more suitable for while you are working in zbrush and just "shaping the…