It's possible to pose a character using Transpose Master and Layers. You can specify to Transpose Master to create a new layer for the pose for each subtool after you've finished posing. When you want to work on your model in the A-pose, you can hide the pose layers for each subtool, returning your character to the A-pose and allowing you to work with symmetry on it. Re-enabling the pose layers then shows your posed character with the new sculpt work you've done.
But a workflow that includes retopo with ZBrush posing... Hmm I'm not sure.
I've found that for the most part I prefer to create a base mesh using the Skin modifier in Blender, split it into separate objects, clean it up so that it requires pretty much no retopo (if at all), then import all into ZBrush and work on it using subdivision. I only use dynamesh for the face and hands which will require retopo anyway, but I don't really use it for clothing unless I need to create holes in the geometry or something.
Or another option might be to work up a decent model in ZBrush from ZSpheres, without fine details (a sort of base mesh if you will), import into Blender and retopo + UV, export back into ZBrush to work on fine details, then use Transpose Master with Layers for posing. You can bake your details by unwrapping using UV master using the seams you marked in Blender.
You can try a type of retopo in ZBrush using the ZRemesh Guides Brush and ZRemesher, and UVing like this, although I haven't had much success getting decent results.
EDIT: BTW, I use the GoB add-on (click on Download) for Blender to import/export between Blender and ZBrush.