Ugh I'm so confused. This will be my first time renting a car, and I have no idea how much driving we will do to and from Universal and one day at MK. I also don't know anything around the area or where the heck the gas stations are. What the heck do I do??????
Right now, go online and sign up for the frequent renter program of the company you are renting from. No charge for this, and the most important thing about it is that it stops the hard sell tactics you will otherwise get when you pick up the car. Club members don't get the upsell routine. You put your DL on record, make your default choices about fuel and insurance, and those are used unless you change them. It's super-important for someone like you to do this, because if you are feeling confused now, you can't imagine how confused you will get when you are already tired from traveling, and the rental clerk brings up all kinds of doomsday scenarios to scare you into buying lots of extra-cost optional services. Failing to resist that whole up-sell speech with a firmly repeated "No, think you! No, thank you., No, thank you ..." can easily quadruple your initially quoted price. Making these decisions at home without pressure will make you feel a lot better.
Second in importance is this: DO NOT purchase an upgraded-size car when you pick up your rental. They push this hard only when they are out of the size that you reserved, but the deal is that they have to upgrade you for free if that is the case (well, unless every single car on the lot is currently reserved for someone else that day, in which case up-selling isn't feasible, either.) However, the company would prefer that you PAID for the upgrade, so they will always try to sell you one before they admit that they are going to have to put you in a larger vehicle.
Also, well before your trip, get a map of Orlando. (Yes, a real paper map. You can mark routes on them and they will never run out of battery!) You can get them free at AAA if you are a member, or buy one at any bookstore or online. If you don't know your way around, it is important to study up a bit, because standstill traffic jams on I-4 are extremely common, and you will want to know what your detour options are. Orlando has so many small lakes throughout the city that roads have to go around them, which makes alternate routing a bit tricky. Once you know where you will be going and where your hotel is, you can easily estimate about what your total mileage will be. A lot will depend on where your lodging is, but we normally drive the equivalent of the corridor between USIOA and WDW daily when we are in town, and on a 5-day trip we very seldom use more than 1/3 of a tank if we do not leave the Orlando metro.
BTW, if you will be heading directly to the airport from USIOA, the routing is tricky. This is one time when you won't want to follow the signs out of the parking garage right onto I-4, because then you have to go through the airport to gas up. The way to go when you exit the parking garage is to go south on Hollywood Way, initially following the signs for Royal Pacific Resort, but not turning off at the hotel entrance. Hollywood Way soon intersects Turkey Lake Road in front of Dr. Phillips High School; turn left on Turkey Lake and follow it until you come to a major intersection that has gas stations on both corners, which is Sand Lake Rd. Fill up, then turn east on Sand Lake. At this point you have two choices: you can either stay on Sand Lake until it changes name to McCoy Rd and takes you into the airport via the ground route, OR you can almost immediately take the I-4 West ramp from Sand Lake onto the interstate, and then exit east onto the Beachline toll highway straight into the airport. The Beachline is always faster once you get on it.