By the way, I love your project, and I'm thinking of doing something similar. Here's what I would change:
-Cut a circle out of the metal lid, but replace it with a piece of plexiglass. Silicone the plexi to the inside of the lid. That way, you have a clear top, but still reduce evaporation. Maybe drill a small hole in the plexi for easy feeding.
-Lees makes a couple of small, round UGF's for bowls. I have one of the 1G and one of the 2G each. Depending on the dimensions of the jar, I might use one of those or cut my own out of a larger UGF. I would turn the elbow around and cut a hole for it in the UGF. When you drained the water, it would siphon out all the gunk from under the UGF.
You mentioned you want to plant DHG, so a UGF wouldn't be the best choice for that. In mine, I'd probably use stem plants and moss. Anyhow, love the blog and I'll be following your progress.