Ya you have too many of the most basic questions. The 2012 is a great jeep and the 3.6 is an improvement over the 3.8.
You want a Sahara, thats a start. Welcome to the forum. Look around, read up. Using google is great, most searches will lead right to this site anyhow.
You will find out that there are more cost effective ways to go about doing things-a right way and a wrong. People are here to help.
There's is a lot more to it then "I want bigger tires and rims" best advice-- buy the jeep stock and drive it for a while. Decide what upgrades you want to do, then if you have question, you can ask away.