Ok, after more reading and thought, this looks to be an acceptable direction....
1. Returns at one end of the tank. One enters the tank below the overflow box with a 90- degree elbow to point down the back wall. One enters the tank through the overflow box with a 45- or 30-degree elbow pointed toward the front wall of the tank.
2. The two primary drain lines located at the opposite end from the returns, with the emergency drain at the return end of the tank.
3. Drains into filter sock for mechanical filtration (chamber#1=6" wide)
4. Baffle (1") then pot scrubbie bio-filtration (chamber#2 = 6" wide)
5. Baffle (1") then refugium (chamber#3 = 15" wide)
6. Baffle (1") then return area (chamber#4 = 6" wide)
1. Dual returns will allow me to keep a high turnover (dual pumps ~1200GPH, closer to 900GPH with head losses; still more than the usual recommendation of 10x capacity for turnover in a planted tank)
2. Why separate the drains? It is conceivable that a plant or large leaf could become detached, float into the overflow box and clog both the primary and secondary drains. If the emergency drain is in the same vicinity, a remote but plausible possibility is it getting clogged as well. Placing it on the other end reduces that chance.
3. The filter sock method should allow for easier maintenance/cleaning.
4. Enough room for bio-filter? Total scrubbie volume is ~6x12x12" (0.5cu.ft.).
5. Refugium will be for breeding the shrimp, also heavily planted.
6. 6" might be too narrow to fit the return plumbing/pumps and the heaters nicely, not a big deal to move the baffles if this is the case.
Moving on to other items (like pipe size calculations and sump overflow calcs), but still readily accepting input. Thanks thus far!