Thank-you. I've only looked in NifSkope right now (not at my CS PC, so no textures or anything), but it looks perfect

I'll confirm later, but looks fine

OK, ther's a slight issue: all the faces seem to be reversed: textures from inside are on the outside... I saw the option to fix this recently, but can't seem to find it-- if you just tell me what to look for, I should be able to do it myself 
OK, I found how to do that, but hit one last issue-- most of the Faces invert fine, except for bits on the Support Beams, and the interior of the Fireplace... They all seem to be part of a much larger Mesh which incorporates everything, and inverting the textus stil has no effect-- here, the textures seem to be completely gone...So, after some fiddling about, I had another go at the Mirroring, and managed to get it working myself

(Yes, I'm very pleased about that! [Laughs])-- the problem is, now everything LOOKS fine in Blender, but I CANNOT Export the .nif file... When I try, Blender either finishes instantly, producing an empty .nif, or takes about 30 seconds, and produces 2 parts of the Mesh, instead of the whole thing... any ideas?