After winding about a mile of wire onto a P90 bobbin, I had two fatal problems - the start hookup wire broke off while I was taping (bad soldering job I suspect, easily remedied next time)
The bigger problem though was realizing how loose I wound. Also discovered as I was taping; the coil bulged out from under the tape. This will not be so easily fixed, and will probably take some practice to get the right tension to avoid too much slack *and* avoid wire breaks.
<note to self: don't quit your day job... yet>