I have stayed there once, heading back for trip #2 in 20 days!

I hope this helps...
1. Can someone tell me the themes of the rooms? Also, can you request a certain theme?
You can see the room themes by clicking this link:
http://www.hifamilysuites.com/kidsuites.html Scroll to near the bottom and click on the themes to enlarge the rooms. Yes, you can request a certain themed room upon check-in. They will do their best to accomodate you, but can't guarantee a specific room.
2. I have read debating thoughts regarding the hotel buses. Is it better to ride or drive your own car?
We are not taking our own car. We will use the bus service and/or cab service at the hotel. We did not have a car last time and won't be renting one this time either. There are lots of posts regarding the shuttle service, if the search option is up, you may want to try it to read other's comments too.

Search for HIFS shuttle
3. If you do drive, how much is it to park your vehicle at each park?
I believe it is $7 a day.
This is why we aren't renting a car:
We need a minivan (4 adults, 2 kids) The best rate using every code I can find with tax and fees is $397.45
We can use a limo and taxis for less... Here's my breakdown ...
Limo $185 with tip
Cab Fare one way every day to the parks $15 x7 = $105
We will use the shuttle for one way each day.
Additional Cab fare Budget (just in case) $60
TOTAL = $350
Mini-van Rental $397.45
Parking everyday at the parks $7 x 7 = $49
Gas $20
TOTAL = $466.45
We are going to save $126.45 approximately by not renting a car. I also won't have the headache of finding the car rental desk at MCO nor returning it.
Of course, everyone is different, so you should ask yourself these questions...
1. Am I going to feel trapped at the hotel without a car?
2. Are we going to need to leave the hotel many times to eat outside of the parks or hotel?
I hope that helped!
