The general rule is that when a spell has multiple effects to choose from, you make those choices during Step 1: Declare Spell. This is when you would choose which conditions and enchantments you wish to destroy. Then in Step 2: Pay Costs you pay the total mana cost required to destroy them. If it then gets Nullified, you are out the entire amount of mana.
Enchantment transfusion is an interesting case. You don't actually target the enchantments that you plan on destroying, so it doesn't matter that they've been moved. I could be mistaken, but I'm pretty sure that Enchantment Transfusion would be pointless and the selected Enchantments would still be destroyed regardless of them being moved. I can't think of a reason off the top of my head at least why moving them would save them, since they are not targeted by the spell, but I'd have to actually look over things to be certain, which I don't have time to do right now.