Cladophora is something that you're only going to develop if you bring it in on new plants. It won't magically appear - especially in a "dry" environment like that. So I wouldn't worry about that. Wouldn't worry about mold, either, as it's something you can fix with a quick spritz of Excel in some water.
To make things fill in more quickly, break those plant groups up and spread them out. Use a checkerboard pattern for planting.
Keep the water line just at the surface of the substrate and mist your tank a couple times a day at minimum. Use airline tubing (as a siphon hose) or a dropper to remove any excess water.
Make sure there are ferts in your substrate - usually in the form of root tabs.