Fondant: Buy it. Making that much fondant to cover that much cake is going to be a trial that I'm sure that you won't want to go through. Country Kitchens sells 5# buckets of fondant; I've heard good things about the taste of the Pettinice brand, and you can always add some of the LorAnn oils they sell to the fondant to add flavor. You will need to do a glaze/crumb coat before you put the fondant on; seriously consider doing a jam glaze (heat to simmer, strain, brush on naked cake) instead of buttercream for that coat.
Freezing: Don't freeze a fondant-covered cake. Don't refrigerate a fondant-covered cake. The condensation that will collect on the surface during the thawing process will melt the fondant. Yuck.
Do yourself a favor - don't do a light sponge cake; with something that large and heavy, you'll need a firm cake. I've noticed that if you add about 1 tbsp of meringue powder to a cake mix that it firms up fairly well. Don't use wooden dowels - get the hollow plastic support dowels, they'll work better.
Another suggestion I would make is don't use cardboard rounds to separate the tiers; they'll soften up. Country Kitchens sells plastic separator plates made specifically for stacking; I have several and I know they'll work well. You'll also need the white plate pegs to secure the stacking plate to the tier on top of it (thats how I do it).
And, for the love of whatever, please get a good, heavy, thick board to put the main cake on. I *think* that an filled and iced cake of the size you want should be VERY HEAVY. By the charts on the Wilton site and on Country Kitchen:
*You're looking at the equivalent of 13 cake mixes for just the main cake, based on 5 cups of batter per mix (65 cups of batter). I don't know how much a cake mix weighs after baking, but guessing that it'd be about 3 pounds, that's about 39 pounds of cake.
*Your cake will be wearing about 13 1/2 pounds of fondant (you'll need to buy extra to have some working room)
*With only one layer of filling in each tier, that's about 2 pounds of sleeved filling for the main cake. With two layers of filling, that'd be 4 pounds.
None of that includes the crumb coat, the internal structure, decorations, or anything else.
Your *main cake* should weigh about 56.5 pounds, and about 60 pounds after internal structure and decorations.
I'm not by any stretch of the imagination trying to discourage you; I think you are an incredibly gutsy lady for wanting to tackle this, and kudos to you! You mentioned that this was going to be your first cake, so I just wanted to let you know what you need to prepare for.
Best of luck!