You just move the IAC from the 2.5L TB to the new TB. Other than that, the ECU will adjust itself (it takes a few days for it to do it right, but it will do it all by itself).
As for enlarging the intake manifold opening, it is not 100% necessary (you WILL feel the gains with the new TB, especially throttle response in the mid range, but you will not take 100% of the possible benefits unless you do it). Now, it is important to note that with the 2.5L, you cannot expect HUGE power gains from small mods like this; I have even more mods (read my sig), and the difference IS felt, but it is still not like having a 4.0L under the hood... Just so you are not expecting more than you will get. Overall, would I recommend this mod? ABSOLUTLY!