I'm now a previous cruiser with Carnival but where would I find my Past Guest number?
It should be on the bottom left of your Sail & Sign card. If not, follow the instructions here.
I am all for using a Travel Agent that specializes in cruises. It doesn't cost any more to use one, and they have a world of knowledge, and guidance to offer you. I would look for a reputable one in your area. I would rather have an advocate on my side should there be any problems.