Your project seems poorly thought out to me. Building up floors is tacky. Adding more length for hot water to travel isn't practical. Leaving extra wire that's unnecessary in the attic is amateurish. I sympathize with needing more closet space - everybody does, it seems.
Without seeing a floor plan and examining things, I have no idea if you're dealing with bearing walls or just partition walls. These are things you need to consider.
Chances are, there's a better way to move the water heater, or that it would be better to pull up carpet and saw some concrete. The end result would certainly be better than having a raised floor to trip over.