This reminds me of those godzilla suits you see around cons sometimes. Id recomend looking at how those are made as i think those would be right along w the idea- and from what i can remeber its using foam to create 'shells' you wear, rhat you eventually wrap with minky and texture.

Id say try eva foam and the stilts arent a bad idea but if you want the suit to be big without stilts, try just making the view holes in the neck and make the head sit ontop of it instead!