Hot water heaters are always rusting and then leaking. Corrosion is always a problem with water and metal, along with sedimentation and the growth of slime.
With the box of rocks, yes you'll need to duct hot air in to heat them, and duct cool air in to extract the heat and blow it through the house. I don't know that this needs a beefy system, if you've got central air there is already most of the duct work in place.
With the box of rocks, yes you'll need to duct hot air in to heat them, and duct cool air in to extract the heat and blow it through the house. I don't know that this needs a beefy system, if you've got central air there is already most of the duct work in place.