Yeah, we're definitely taking the Coho. It gets me to a Jack in the Box the quickest LOL. I miss living in the states when it comes to good fast food.
If you like good fast food, then you must make sure to include In-n-Out Burger several times on your drive. We driven from Vancouver, WA to DL a couple of times over the last two years, and In-n-Out Burger pit stops are an essential part of that drive. We make sure to carry the list of locations with us--the first one is in Redding, lol.
I second everyone else in that at the end of September, you should be fine without reservations in the smaller town in northern CA. Having a list of several to choose from in various towns is a good idea; we also carry a
AAA or similar travel book with us so we have lots of options and phone numbers handy.
I totally agree with you about preferring to be in the parks late at night rather than early, but keep in mind that the parks tend to close earlier during off peak times. On weekends, they'll probably still be open until 11 or midnight, but on weekdays they will likely close around 8 or 9. Also note that the Halloween parties will probably begin around the end of September, and last year DL closed at 7 on Halloween party nights.
If you are there on a Halloween party night, that might be a great alternative if you are unable to add a day to your military tickets. It's cheaper than a regular one day ticket, the park will be open until midnight, the crowds will be low, and there will be a lot going on that you won't get to experience on your regular park days. Look for more info from Disney and on this site as your trip gets closer.