I recently moved into a new house...NEW to me but built in 1953. Its a ranch, but at one end there are two shallow steps that lead into two bedrooms and a bath. My question pertains to what is beneath that, I have a full basement under most of the house but where those stairs are the full basement stops and there is a crawl beyond that...As of right now the crawl has a plastic vapor barrier on top of what looks to be a dirt floor.The plastic is stapled to a very old wooden frame, but the wood is so old that it is rotten and falling apart...

Question 1. Should I remove everything and build a new frame? do I need a wooden frame? can I just cover the dirt with plastic and be done with it?
The ceiling of this crawl is insulated but the walls and floor are not, there are also two metal grates(vents) which let an enormous amount of cold air into this area.
Question 2. Can I close off these vents or will that lead to mold growth..Reason I ask is with this area beneath the bedrooms they are constantly cold.
Thanks to anyone that can lead me in the right direction, Ryan.