If you want to wake up every day to poo on the floor and a missing bunny, forget the top. If you want your bun to stay safely in his cage where he can't chew any dangerous wires or get into tangles behind the fridge, put a top on.
Buns can jump really high (you'd be surprised) so a top would be best. You don't really need extra levels, but they would add more space and interest for your bun. I recommend it.
If you have cats or dogs, you need a sturdier cage. However, if there are no other considerations, great cage!