Since damage to both players happen at the same time, it's up to the player whose turn it is to choose in which order it is applied.

Paying 2 Fire Mana is a condition for the damage to happen.

Note that now, EVERY spell you have on the board is now a wildfire.

"All your spells are now copies of Wild fire" also implies "and for the rest of the game". Thus if any spell tries to enter the board after this spell is activated, it's now a wild fire.

Note that since your Animal is not considered as a spell, it remains unchanged.