If something, the previous silver age stuff doesn't add too much. You can start with the first Moore trade, because several of these issues features fragments of the original series. The first Moore story starts with a strip of that kind to put the reader in context about what is the story.
You don't need to read everything before that point. Specially considering than several of the old Marvelman tales were Captain Marvel(Shazam) stories, adapted. Honest, if not by Moore deconstruction, Marvelman would not be nothing but a forgotten curiosity.