I bet you get different opinions for each question, but I can offer some advice on the bonding part. Silicone absolutely will never stick to the baffles, so you aren't really "bonding" them in place. At best the silicone acts like a bump or ridge behind the baffle and basically jamb it in place due the flow. The silicone will bond to the glass beyond your wildest dreams and give you a nice spot that grows algae and is hard to clean. I've never used epoxy in this way, but I'd expect it won't hold on to the glass over time, and some epoxy might have some chemistry that you wouldn't want in your tank. The last 40B sump I built was different in that the baffles slide in vertically and rest up against glass strips that are bonded to the sump with silicone. This joint will last forever, and the baffle is easily removed if layout change or a deep clean is due.
On the topic of a sponge after the fuge, without one its certain things will get out of the fuge and into the pump and display. This gets real fun if you run Cheato and start chopping tiny strands into tinier strands that you'll be picking out of the tank as it pops out from everywhere. I believe there must be a sponge just before the return pump chamber. The problem is what happens when that sponge clogs and the level goes up around the skimmer. My first sump was Fiji Cube kit and they make nice stuff, but the design has a flaw in this situation. The final baffle is too high and causes the water level to increase because there is nowhere else for it to go. I drilled several holes across the final baffle at the water's normal operating height. These holes end up being just slightly higher than the drop that happens in the sponge/bubble trap slot. If the sponge clogs, the water comes up to my drilled holes and bypasses into the return chamber without swamping the skimmer and creating a black bubble mess....lol
Build your first sump anyway you see fit. I think you'll see after some time different people have different needs and approaches, and what you think you want you'll likely be re-doing in 6 months as things evolve.
My last thoughts in regard to UV output and where to aim it. If you have a manifold in the sump and are using a single return pump it doesn't really matter in my opinion. I personally don't do it that way simply due to the safety of running it as a separate little system with it's own smaller pump. It's unlikely a pump will run forever. It's also astronomically less likely 2 pumps would fail at the same time. By using a dedicated pump for the UV, you can tune the flow rate through it (really important!), and have it on a smaller, separate return to the display. In a bad luck situation you could have a pump fail and still have flow through the sump. It's also awesome to be able to clean either pump and not be all torqued up running around with zero flow going on in a panic....lol
Best of luck!
Kurt J
