>I would've thought that if he put the top as an exhaust, the rear fan would be useless since hot air naturally rises.
It might be useless depending on his CPU cooler. If his CPU cooler works fine and/or is too big- don't put one above the thing.
Not only that what fans are he getting- because if they suck, it doesn't matter where he puts them.
Personally his set-up sounds fine if the temperatures are okay in his room. If it doesn't work as great as he hopes, he can always move the stuff too.