You won't be able to skin the mesh you make yet, or import back to Nif. BUT, you back import a basic mesh into blender, I don't believe the scale will be correct and will be missing materials and skeleton. But useful to create your base mesh for your outfit, ready for when the proper tools drop. Basically just use the export tab in nifscope to export as .obj then you can use a default import script in blender. pretty sure that's the best we can do for now. Edit: didn't see first page, Woah, mesh looks amazing. So yeah didn't realize you already had a mesh. Like I said you won't be able to get it ingame or rig it. But you should be able to match up the proportions.