Re: DIY Rimless Tank this may be a litlle late if you already have the glass, but go for "starfire" (that's a brand name, the generic term is "low iron") It's clearer than regular glass without the green tint. Thiner glass isn't too bad, but there's a noticable difference when you get into 3/8 and thicker.
Everything I've read on building tanks says to put the 4 sides on top of the bottom pane. I have a 125 that I built this way and no issues with the silicone holding. keep in mind that it is not just the silicone shear strength that is holding it in place, at each corner you have an entire seam holing that pane in place.
Lastly, I would reccomend havin all your edges polished. I originally thoght this would give less holding strength but after building it I think it actually increases it because of the nooks it give the silicone to hold onto |