We just got back last Sunday on teh Auto-Train roundtrip.
1. We left MK parking lot at about 1pm. Got to Train at 2Pm. The 7pm dinner was closed out when I got on line. I was about 15 people back. The person right before me got the last 5Pm dinner. So we were the first family stuck with the 9PM dinner. It wasnt that bad for us . We took a nap from about 6-7 and watched a movie after on our portable's before dinner. Seemed to make the night go faster. Boarding starts around 2:45 but there really is no rush unless you just want to get situated. We never had trouble getting overhead space for our carry-ons. I guess if you check in early you will get the seats across from each other but if you check in later like us you run the risk of being on the same side and not able to see each other. We didnt care.
2. I dont know about local restaurants but I see that Longhorn Steakhouse is in Lake Mary about 7 miles away and they are great for a meal. We should have done that. If you have GPS than it will be easy.
3. We brought drinks and snacks because thats how we do it.

There is non-bottled water available and drinks you can buy. The snack they give you when you get on the train is just a bowl of mixed pretzels and stuff....nothing exciting. Whatever they give you on the train gets picked over and messy very quickly. Like when they put cookies out they all get destroyed. They ran out of hot chocolate on the way down before we could get any. We didnt like the adult choices for dinner so we got the kids chicken strips and mac and cheese. I'll say the only thing I thought was edible was the Vegetable Lasagna. Drinks at dinner are lacking.....warm "Iced-Tea" or warm house wine. We tipped at dinner but not at breakfast. I don't think that its like a restaurant and they make their living off tips but they are still serving me so we left some $$$.
4. No showers. Each car has 3 bathrooms downstairs. One bathroom is big enough to change in.
If I ever did it again I would have to get a downstairs car. We got no sleep both ways upstairs. Too many people walking by all night and too many kids screaming and coughing all night. If you have noise cancelling headphones use them. I borrowed my fathers and they were great. We did the trick with hanging the sheets up for privacy while we slept and that worked well. Its funny that on the way down everyone did that but on the way home we were the only one's. Lots of people commented that it was a good idea. That way you get a little privacy and you dont get that breeze on you everytime someone walks by (which is all night).
Best Tip: I dont drink alcohol and I hate wine...but i had some at dinner and it helped me sleep a little
Enjoy.