I'm not sure if you ever completed this project, but I'd recommend doing a liner for the wetland area. And maybe even deeper gravel beds, like 3-5ft...the first bed will be your filter, the second won't do much but maybe de-nitrify some if it's deep enough. Search for deep substrate bed on the internet to find more, but basically the water won't be circulating in the deeper section of the 2nd bed, it will go anoxic and nitrogen gas will be released....flow rates have to be pretty low for effective denitrification, so it won't be optimal for it but will do some.
If you go with fish, avoid bluegills and their hybrid counterparts for swimming ponds....they have a tendency to find nipples and moles very attractive for tasting (especially if they are hungry because they live in a cleaner swimming pond). I'd stick with Yellow Perch, they won't go anywhere near swimmers during the day.
