Some questions about aquaponics in an apartment

[Adam Richards]

Hello,

I am new to aquaponics and really interested in starting my own system. I have taken Sylvia's and Alan's course on it and, having just finished, am ready to get it going. 

I do, however, have a few questions and would greatly appreciate anyone's input on these:

1. I live on the 14th floor of a decent-sized apartment and am thinking of a 40 gallon fish tank for a 6 cubic feet grow bed with a sump tank. The weight totals about 928 lbs. and would span over about 43 sq. ft. Does this sound reasonable or would it be too heavy?

2. I was wondering how exactly I would calculate the volume (and weight) of my grow bed. 6 cubic feet (1x2x3), according to the course, would require 300 lbs. of grow medium (using LECA). The course also said that 40% of that grow bed volume would be water and 60% grow medium. I am unsure of how exactly to calculate the volume of grow media then. Do I figure enough grow media to first fill the bed without water or do I take the volume of the container and fill the grow bed with 60% of grow medium and then let the water fill in the rest of the 40%?

3. How necessary is a sump tank for a system of this size? If so, would an 18 gallon sump tank be a reasonable size for this system. 

Thank you so much. I greatly appreciate it.

Regards,

Adam Richards