To answer a few of your questions...
Yes, you may take food in with you. Cannot be alcoholic bevs, glass container (baby food exception). You may carry a small cooler or medium backpack. Stop by the FAQ's on the WDW site and they give the dimensions of the cooler. Also, no drag behind coolers, wagons, carts.
Dining Plans can only be purchased if you are staying onsite in a Disney owned property. And then you need to purchase it as part of your package (lodging, tickets, and the dining). There a couple of special situations where you don't have to purchase the tickets (Annual Pass or military special rate...) in order to get the dining plans, but you do have to stay in the Disney hotels.
The Dining Plan may or may not be a good price for you. You should look at the menus here on wdwinfo.com or allears.net website and choose what you would really order.
There are quite a few threads that really explain that. You'll want to stop over to search those. I am new here so I haven't learned how to post threads. Definitely read through the sticky posts...
Tickets...Disney tickets are "front loaded" meaning that you pay more for the first day and then added on days are less. So two single purchase tickets will generally cost more than on 2-day tickets. The base tickets are one park per day. If you are hoping to visit 2 parks in the same day, then you will need to add the Park Hopper. It you have a 2 day PH, you could spend a short amount of time in all parks (2 or more each day), but that is not an efficient use of your visit IMO.
As this will be your first visit, you will want to pick which attractions and entertainment are the must do for you and each member of you party. Then look at the maps and decide the best way to tackle it.
Fast pass will be another good thread for you to learn about.
Arrive early. Earlier is always better than staying late.
It can be overwhelming to plan the trip and then to also execute the plan. Remember you WILL NOT do everything. You have to be willing to change your expectations and then you will find pixie dust of all sizes and types.
We made our first (and so far only) trip on 2010. We didn't get to visit all of our must do's but we did find quite a few of the "overlooked attractions" that the veterans have spoken of. And those were by just stumbling upon them!
Glad you are h-ear!
