Jared, I would definitely start them inside, probably about 3-4 weeks before you want to plant them outside (pumpkin plants are pretty tender, so that would be after danger of frost; however, they sprout and grow pretty quickly, so you don't want to start them TOO early). And you should definitely use fertilizer, those giant pumpkins in particular are very heavy feeders. And lots of water, as well. I think I may have read somewhere that people prune the vine once several fruit have set, so more energy goes into those -- although I've never done that myself; maybe someone else here will be able to advise you about that. Keep in mind that at first you are likely to just see "male" flowers, which grow from the vine on a relatively thin stalk; the female flowers will have a very small pumpkin between the bottom of the flower and the vine itself.
Although I've grown lots of squash and "regular" pumpkins, the only time I tried growing the big ones -- and I think it was actually Atlantic Giant in my case as well -- I had one really big pumpkin growing that I was pretty excited about; just as it was getting near harvest time a gardening friend stopped by and I took him out to the garden to show off my accomplishment. Unfortunately, overnight a deer had eaten a hole in the pumpkin and completely cleaned out the inside -- it kind of looked like Cinderella's coach!
Best of luck to you with your giant pumpkin -- I hope you will post pictures for us next year!
