Definitely stick to the malls rather than the same as the next t shirt and towel gift shops! If you've never been before, pace yourself as there's a lot to do I've been 7 or 8 times and never get bored of it out there. If you get lost, make sure you stop at a 7-eleven or a branded fuel station not just stop and ask someone as there are some rough and dangerous areas in Florida but generally people are polite, friendly and the complete opposite to this country, maybe the weather has something to do with it lol.
Food wise I'd not bother with hotel food, food in almost any restaurant is cheap apart from the high end exotic places. Also make sure you drink plenty throughout the day as the heat can creep up on you. Food portions are also large, so you can save money on sharing one large portion for lunch. Also make sure you have a meal and some cake from the Cheesecake Factory and if you like or even if you don't, try the peanut butter chocolate deserts/bars you'll be hooked!
Oh and if it says your sitting in a splash zone, you WILL get wet lol. Even if you look old enough to drink, take some I.D with you when you go out as without it you may not get served.
YouTube videos of the rides is a good insight to what to expect and also check out the OVN (Orlando visitors network) site.
More importantly though, relax, take in as much as you can and I guarantee you'll be counting the days until you go back before your even home again!