I'm an old hand with visiting WDW but my first DL trip was a challenge. Thanks to the wonderful people here, I learned alot and everything worked out fine. I understand your questions about distance. I simply could not grasp the thought that you could actually "walk" from your hotel room right over to Disneyland. What helped me the most was using satellite pictures. I would map a distance in my own neighborhood and then map that distance using a satellite photo from a hotel. That really helped me understand what everyone here was sharing. You might like to give that a try.
Oh and about supplies, I stayed at the HoJo several times and they have the best "convenience store" I've seen. They even had OTC toothache medicine there. (And they have some snacks and I believe PB&J stuff. I haven't been recently so maybe some others can chime in.)