DME would add some maltiness that sugar would not. but I don't think that such a small amount would actually make 5 gallons that much sweeter.
Food grade means that no odors from the plastic itself can leech into the contents...that the plastic is inert basically.
I would not ferment in a garbage can because there's no way its food grade plastic.
Primary: English Mild
On tap: Pale Ale, Lancelot's Wheat, English Brown Ale, Steam Beer, HoovNuts IPA
Bottled: MOAM, Braggot, Raspberry Melomel, Merlot, Apfelwein, Pyment, Sweet mead, Cabernet
Gal in 2009: 27, Gal in 2010: 34, Gal in 2011: 13, Gal in 2012: 10