1 - as far as I can remember someone has asked something similar and I think that it doesn?t, pretty sure it doesn?t.
2 - Would think so. See no reason why it shouldn?t.
3 - I think the right one would be +65, a a soft leather enhanced with +20 to its DB would result in +40 (Full soft leather suit is +20, magical +20 = +40), this enhanced through the spell with +25 would end up on +65.