I don't know for sure. I do know most "hosts" are repressed , depressed, depleted individuals. A lot of the emotional stuff is being held by other alters.
Yes it is possible to have many many alters, some people call it polyfragmentation, which just means the psyche split into a very large number of alters.
Yes, it is possible to appear mostly normal, I have DID and to my colleagues I mostly come across as reasonably normal, they really wouldn't have any idea I have such serious psychological issues. They have no idea at all that the person who mostly stays glued together in the work place (mostly) dissolves into a dissociative mess the second she walks out the door in the evening.
My pain is hidden. Primarily from myself, but definitely from everyone else too.