Welcome to the forum! In answer to your questions:
1. No. The PCM (computer) in our vehicles adapts to the change in air volume. It does take a few ignition cycles + some driving in several different modes (cruising slow around town, cruising at freeway speeds, a few WOT blasts
) to get it there.
2. An aftermarket CAI may void a warranty if it is the direct cause of a failure or damage to an OEM part or system. So, if you get a CAI get a good quality one and stay away from the eBay cheapies. There's more on buyer and seller rights with respects to warranty under the Magnusson-Moss Act. I purchased an AFE CAI (good quality I might add) and it works great. Got an end of month deal directly from them. Don't remember the exact cost but it was less than $200 with shipping. I installed it myself...it's an easy mod to do.
3. The MOPAR catback is a nice unit, made for Dodge by Borla or Gibson - not sure - and sounds pretty good. Pretty dang expensive, too. You can get a catback of the same quality for a lot less. And you don't really need a full catback (IMHO) if all you want to do is improve flow. All you need for that is to get a freer flowing muffler.
So good luck with the mods and just keep askin' those questions. We don't mind helping out.