Restarted for version 2 this month.
Cut the 'window' in the 5g bucket, made it large. Marked on bucket w/sharpie, at the outer-edges of the lexan sheet held about where I wanted it. Then marked corners in from that. Used a dremel to not-quite-cut-through the plastic along the lines, and used a knife to slide along those dremel'd grooves. Smoother edges that way on the window-hole.
Siliconed the window to the window-hole, on the inside. First try, leaked at a corner. Second try added more at the leak point, but didn't fix it. Third try put silicone around the entire inside edge of the lexan, fixed!
Filled with water, let sit overnight, no leaks. Setup next to the Aqualibrium system, so its in my face to get looked at and checked on and fish fed. Hopefully I will have it running in a couple-three weeks. It'll be staring at me to finish it.