First time Sump building questions

I would avoid crushed coral. With no predators in a LR fuge, you'll be buzzing with pods. Throw some chaeto in there if you want them to have cover. Or lots of rubble rock.

For the glass that might be OK and yes the silicone will bond well enough to keep it in place, very well. Just scrape glass and wipe with denatured alcohol before applying the silicone.

And remember to get momentive RTV silicone only. From Grainger. Then you also need to (or, you really should) let it cure for 2 weeks

 

This stuff

http://www.grainger.com/product/MOMENTIVE-RTV-Silicone-Sealant-4UH12?functionCode=P2IDP2PCP

 

Cure time, yes. That is time until is it cured enough to put water in it and test it. But talk to any reputable glass aquarium builder and they will tell you the same thing. 2 weeks to reef safe. It takes time for the silicone to fully cure to the point where it is not longer leeching anything into the water column.

You can go ahead and fire it up before then, and sure, many have done so, but you are rolling the dice on whether or not you will kill off something in your system.

Ever since I learned that 2 week thing, I always make sure I tell people - better to say it and be ignored than not to say it and be blamed later.

Same thing applies to acrylic tanks BTW. 1/2" should sit for 2 weeks before being exposed to water, 3/4" 304 weeks, and 1" or more should really sit for 2 months without anything beyond a test fill. But no one listens to that one either, at least that one doesn't affect the contents, it just affects the seams over the long term if you don't wait. I'm full of information most people don't want to hear tho...