wet/dry filter?

Hello!
I plan to convert my current saltwater tank to freshwater, the tank already runs with a sump, which I intend to keep. The sump is 120*40*50cm and today has three compartments. It has a waterlevel of about 27cm. But I can change this when coverting.
I´m not sure how to use a sump in freshwater, what media to use? And if i should start a wet/dry filter with bioballs?
It won`t be dificult to change the sump to accomodate a wet/dry filter, but I am a bit concerned about the noice level and the evaporation that the wet/dry filter will bring. The evaporation is one of the reasons why I am converting to freshwater, today I have about 7-9l/day evapotating from the tank, making it hot and steamy in my appartment.... So I want that down as much as possible, but I think remowing the metal halides and the skimmer, slowing down the flow in the tank and putting covers on the tank will do a pretty big difference, what do you think? The question is how much of this that will eaten upp by adding a wet/dry filter?
So what do you say, how loud are wet/dry filters and how much will the add to the evaporation?
The alternative is to just put different medias in the sump and skip the wet/dry filter.

sounds calming, I will proberbly setup a wet/dry section in the sump.
I plan to remove the metal halides, that and reducing the flow and putting covers on the tank will proberbly be enough to push down the evaporation from todays levels (wich is around 7-9l/day). At least I hope so
What´s to think about when constructing the wet/dry? Anything about size, or is bigger always better? The tank is 720l, I think I will fit 20-25l of bioballs, how does that sound?