I wired a Skyzone TS5823 video transmitter to mine. You can easily connect it to a GoPro or Xiaomi Yi but there will be about 1 second of latency, which is not ideal for FPV (but great if you just want to have a monitor to look at while flying LOS).
To wire it up, the Phantom 1 has two power leads that come out of one of the legs. Just pull them through. They run the same voltage as the battery (around 12v). Then you'll need to solder on the vTX. After that, connect up your camera. If you need an FPV camera and transmitter, the FPV kit at Miniquadbros works great as well, and you only have to solder the vTX.
For upgrades, don't worry about the props for now. Just get used to flying it. I use the props with self tightening nuts and they work well. I've had the Phantom for almost 6 months and never so much as chipped a prop yet. Learn to fly manual mode once you are comfortable. If you're going to fly manual you should get the propeller guard.
Other than that you may also need larger landing gear. I find that the stock landing gear wasn't quite high enough so I got bigger ones. You may also want to eventually get a Gimbal so your footage from your GoPro is more stable. Don't cheap out too much, expect to spend at least $100 for a nicer one. I got the $50 one and it doesn't work very well.
They do just DO NOT use the longer screws it comes with, or you will strip and destroy the motors apparently. I ordered these for my new P3 Pro
http://www.amazon.com/Summitlink%C2%AE-Professional-Disconnect-Propeller-Protector/dp/B00RFX2L6G
Spot on with the carbon fiber camera guard, but I use different prop guards that are the snap on / off variety to facilitate transport of the phantom.
There's a couple on there...