Sump Biulding

Whatever you do, don't use the silicone you get in the big box or hardware stores. Order some GE RTV-108 form Grainger, it's cheap and aquarium safe.  Also you need to let it cure for 2 weeks.

 

What specifically are you looking for?  Make it to fit the equipment you have. There are countless designs that all work well. As for glass thickness it depends on the design. Is it going to be holding water pressure, or will water height be equal on both sides of the glass? I think I went with 3/8" on my sump. Just didn't trust window glass.

 

Are you making the whole tank from scratch, or are you just putting partitions in a standard 75 gallon? What are the functions of the 3 chambers as you are planning? Functions will determine sizes of glass. Your first post is pretty vague as to what you are doing with the glass. Hence all the questions to try and give you better information.
When I did my sump I got the glass at Allied Glass in CR. I put partitions in a 125 and used 3/8" glass.

 

I don't have time to crunch numbers, but if you figure out the volume of water that will be in all the piping you can get a good estimate on the number of gallons that will backflow into the sump. If you know that you can figure out how high you can make the partitions. Just leave a little extra breathing room in there. I run the refuge section of my sump pretty full. The skimmer and return section are a lot lower water levels. But then again I am only draining a few feet of piping.