Not a guru, but I just purchased the kit and had it installed by a pro...$200. It took close to 3 hours for him to do. I am sure it would have taken me at least double that! On to your questions:
1. Some Titans are prewired at the radio head unit. I would assume since you have a LE, your radio would have the connection.
2. The factory system is a 7.8" LCD screen in the overhead compartment and a seperate DVD player that can be put in the center console. I had to put mine under the seat do to having bench seats.
3. I would take a look at the following links for install tips...it should be a lot easier for someone with the center console and the head unit connection.
DVD Install 1
DVD Install 2
I would look at the following to purchase:
DVD Purchase
DVD Purchase 2
Have fun...It is a great system! My kids love it!