Hi, it's fine for him to eat any hay he wants, you must however cover the floor of the cage as prolonged exposure may cause a complaint called Bumble Foot. I don't have a Chin....I keep Degus, but their housing requirements are the same. I cover any meshed flooring with card, wood lino tiles and terracotta tiles [just happened to have some laying about] all of these need to be cleaned/replaced as needed. Try the forum Pat has listed....it'd pretty good.
Lisa x