It's always a good idea to bring at least two pairs of (very broken-in) shoes for each person. That way if it rains, you have dry shoes the next day. Use moleskin and bodyglide to prevent blisters (I wouldn't use band-aids on blisters, as a previous poster mentioned - they slide around too much. Moleskin is much better.). But the first aid stations do have lots of stuff including aspirin, stuff to put on bug bites, etc.
I won't address the backpack issue on rides, since a PP has addressed it already.
Regarding water bottles, I found a great solution last trip. Instead of lugging around a heavy water bottle, I found out that you can just ask for a cup of ice water at any counter-service restaurant (you don't have to buy any food there to get water!). I stopped carrying a water bottle altogether after finding this out.
Regarding Sci-Fi, always take what you hear about a restaurant with a grain of salt. Everyone likes different things, and you'll read good and bad reviews of every restaurant at WDW. I say, if it sounds interesting to you, give it a try!
Keep reading these boards and dig into some of the posts - you'll find out tons of great advice.
