I've tested this, and I did get an error message saying there was insufficient memory on the scratch disk when I tried to make a 100 in. x 100 in. file. If you have multiple drives however, you can perhaps change the drive in the Edit->Preferences->Performance tab. However, since you're most likely not creating a composition that is 8 ft. x 8 ft., you might not encounter any problems. Also, remember to set your pixels per inch to 300, you probably knew that, but I wouldn't want to see an image as big as you're planning on making at 72 ppi.
Just a point worth noting, large format printing is rarely done at 300 dpi, depending on what you are printing on the dpi will range from 72 to 220. Also older versions of Photoshop and a lot applications for handling and printing files won't cope with files over 2GB.