A LOT of newbies lately! Okay, the answer to your questions is....no.
1. When you say 1800 watt system, you are talking about your car audio system, right? You didn't mean you were going to hook something to it that uses 1800 watts, did you?
2. It will not do AM/FM radio, GPS, or OBD-II. You must buy separate components and software to accomplish these functions. AM/FM radio on the carputer is generally not as good as a dedicated head unit.
3. You will need to buy a GPS antenna and software (can be had for around $130) to use GPS. GPS is provided free, courtesy of the U.S. government. Okay, your tax dollars paid for it, but you're paying no matter whether you use it or not. There is no license fee required.
Your system will come with lots of wires. Are you confident in your ability to connect them properly? At a minimum, you will need to get to 1) a 12 volt + line that is always on (called "unswitched"), 2) a 12 volt + line that is switched (that is, come on when you turn the ignition on and goes off when you turn it off), 3) a ground wire. You will also need to figure out how to wire the sound out from the computer to the stereo system.