Some wires are better than others, I suspect you may have some not so good stuff. 1/8" is a tight radius but decent wire shouldn't object. Scratching may occur when you remove the nails and really doesn't matter as nothing will touch the scratched bits.
Too much tension can sometimes lead to crazing of the wire coating but your creasing sounds a bit different from stretching.
It is certainly good practice not to wind directly on metal but as long as the nails are smooth I wouldn't expect any trouble. PTFE sleeving over the nails should prevent any damage and let the nails come out easily.
With winding on a really tight radius I would normally be more worried about stretch cracks on the outer side of the wire but you would never see that unless you looked at the first layer.
Not sure what your wire sources are like, some of the imported stuff here in UK is not as good as it might be compared with the stuff we produced before our industry virtually ceased.
Flux