I understand characters and logos are covered by copyright.

But what about "accessories"?
For example, Snoopy's doghouse, backgrounds associated with video games, game controllers, the Disney castle, a specific Nascar car?

I guess I'm asking, "how far can I go and still be legal?"

I don't know the answer to your question, but I wanted to say, WOW good question!
I would think that it's all probably under the copyright, but I don't know anything about law.

I am taking a guess here but I think anything that looks close enough to be a certain brand, whether it be Playstation, Snoopy, the Chair from Blue's Clues, etc. would fall under the copyright umbrella.

Now how "caught' you are going to get for doing the doghouse from Snoopy, I have no idea. It's like Clifford stuff, most of it is just dog stuff, not very unique. But technically Steve's chair is rather unique and therefore identifiable, which is probably the whole point.

I think cakediva is right. Like I have done several Mickey Mouse Clubhouse-ish cakes. But I will make sure to change up certain things. Like change the door to be Red instead of Yellow make the shoe yellow but change the trim to be red or blue instead of white. It won't be a dead on One of a Kind work of art like the original but everyone in the room gets the just of what is being portrayed. Not that I think the cake police are looking for me but I just always figured it is better to be safe than to be sorry?? You never know when the green eyed monster is at a party or in a room where your cake has been delivered! They might just report ya to someone. I dunno.