he takes everything very literally ... yet he has a great sense of humor? Is it possible for Aspie child to have a very good sense of humor?
Yes. Punny, jokey, and wry are all very possible flavors.
he has a super wild imagination ... I always hear from his room this loud conversation he's having with himself being all these characters he comes up with (or trains, cars, etc.) ... he can be lost in his imaginative play for a very long time ... I thought imagination is something people with Aspeger's don't usually have?
You might look at the book Parenting your Asperger Child by Sohn and Grayson-- they describe "types" of children on the spectrum, including one they call "Fantasy Boy" (or GIRL, I want to add)-- an imaginative type, a bit dreamy, whose inner life is grand and well peopled.
DeeDee