With most of the epoxy applied, the next step before assembling was to glue the glass panels into the front frame. From my dismantled 55gal tank I had two 48x20" sheets of untempered 3/8" glass, which I beveled a little bit with a sander to prevent nasty cuts. The cutout in the front plywood sheet was 46x18", leaving 1" of overlap and glue surface all around.
This one got a bit snug and I had to use some weights to push it down onto the frame. The lesson I learned here was not to put heavy buckets and such on an unprotected glass surface, because it will leave some very ugly scratches.
Luckily this was the lower tank which isn't going to be a showtank anyway.
For Silicone, I chose the cheapest, DAP 100% Clear Rubber Silicone Sealant. I could have gone with GE RTV108 (or 103) but I think this isn't really necessary in this situation. In another thread it was mentioned that the glass needs to be joined with the industrial strength silicone in 2 minutes or less, and I am not that quick in applying it.
To prevent the weight of the glass pushing out all the silicone between glass and epoxy coated wood, I cut short sections of silicone airline, cut them length-wise, and duct taped them to the front frame. This worked pretty good. When the silicone was dry, I just pulled them out.
As you can see, I also taped off the sides of the glass to make removing the spilled out silicone a bit easier. I haven't done this so it remains to be seen how difficult it will be without pulling any silicone out of the seam.