First of all welcome!
Look over the threads and you will find a huge amount of information on everything you wat to know about the Fort.
I would go ahead and book as soon. You can always cancel later if the need arises.
First thing to know is that Fort Wilderness is a big place - about 1 mile from end to end.
Look at the Site Maps thread
http://www.disboards.com/showthread.php?t=2175507 at the top of the Camping page and you can see a satelite view of the entire campground with all the sites and areas marked. You will need to download Google Earth, but it's worth it.
There is also a Golf Cart Rental Info thread
http://www.disboards.com/showthread.php?t=2148754 which shows the prices and other cart info. You will even find a couple of off site rental companies with great service and lower prices than the Fort.
There are three main areas of intrest around the Fort.
The Meadows area has the pool, campfire and other attractions. It's located near the middle of the campgrounds.
The Setlement area has the lake, restaraunts and the boat transportation to other resorts and the Magic Kingdom.
The Outpost area has check-in and bus transportation to most of the other parks.
There is internal bus transportation between all the camping loops and all of these areas so getting around is pretty easy.
When you make your reservations let them know what your requirements are - close to bus or restrooms, etc - and about the heart condition - and they will do their best to accomidate you. As to which loop is best for you depends on what equipment you have and what you want to be near.
Do some reasearh here and you will learn fast and have a great stay.