I'd have sculpted it out of extruded boxes. It's a base mesh, it doesn't have to be perfect. Honestly man you've been working on this for almost 5 months now, just even out the topology into squares and start carving away at it in zbrush/mudbox.
I need to make it good for sculpting.. So on the ref you can see there is this sort of flap on the top of the coat and seams at the shoulders. How do I do that in a way that it is perfect for sculpting? I faced the same problem with the lapel, and ended up making it a separate object from the coat. In the left pic I…