Secondary blues

[Hhchicken1-at-aol-dot-com (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

It isn't possible to wind a secondary with more than one layer, is it?  Also, 
how bad will the loss of efficiency be if I make my secondary much taller and 
thinner than normal, say 1.5" diameter and 20" height?  I'd go shorter and 
fatter, but the only wire I have is .56mm (don't know about SWG) and I don't 
have much of it (free surplus from a rewind place).
What exactly happens if the wire crosses over a little, does it arc really 
badly? I'm not very good at winding coils :)

Thanks for any advice you can give,
    Henry Hallam