Quandary: tank configuration for marine

[Canoe]

I got a used 72"x30"x30" glass tank, ~280g.

• It's got two ~3" wide glass strips, one inset down each side at the top, for a euro-brace type side strengthening. There are no cross braces.
• There is a glass overflow box with around 20 inches of linear overflow, in the middle of each end, for a total around 40" of overflow (when I do the math, and remove the overflow-boxes, I get an internal water volume of ~254g).
• There are two holes in the bottom of each overflow box. I haven't measured, but after a bulkhead is installed I suspect it will be a 2" hole. I figure one in each overflow-box will have to be dedicated to drain, and the remaining two can be for returns.
• We don't know if it is or isn't tempered; drilling new holes...

The seller styled this as suitable for viewing from both long sides, be it in a wall or even in the middle of a room, and, of course, for my plan to place it along a wall. Plan on fish, ~2" sand, live rock in display and sump, fuge in sump. Other inhabitants interested in are: frogspawns & feather duster types. Once established, intend on adding a Mandarin pair. In time, if I can get the chemistry stable, I'll probably add some more corals.

The plastic trim at the bottom is damaged at one end. From what I understand, I can either:

• repair/replace the plastic trim and hope I did it right and it doesn't result in a point load, or
• remove the plastic trim and set the tank on the stand on a 100PSI pink foam insulation gasket.

Is ~40" of overflow sufficient for a 280g marine setup?
How much better would 70" of linear overflow be?

How many galleons per hour for a 280g?

After two holes are used for drains, the remaining two are return bulkheads and can accommodate four return runs by running tube-in-tube through the bulkhead. I like the idea of an Ocean Motions to vary the flow in the tank.

Water flow:

• use the four returns for closed-loop and run return-from-sump over the top, or
• run return-from-sump through an Ocean Motions through the bottom of the tank?

The quandary: I can run the tank

• as it is, with the existing overflow end-boxes,
• add a coast-to-coast internal overflow box (to get ~70" linear overflow), feeding the overflow to one of the existing overflow end-boxes and removing the remaining one,
• add an external coast-to-coast overflow box, add 3/8" thick glass around the perimeter to let the tank overflow over the bank, remove both existing overflow end-boxes, ( this also frees up all four holes in the bottom of the tank),
• sell this tank and get one in the configuration I want.

[Canoe]

How many galleons per hour for a 280g?

Gotta love spell check...

[Vincenzo.]

as for flow get 2 x MP40's upgraded to the max. plus returns from sump.

[Canoe]

as for flow get 2 x MP40's upgraded to the max. plus returns from sump.

thanks,

so power heads running at 3000 each for flow
and and then ? gph cycling through the sump?

what's the current draw for a MP40 running at the max?


p.s.
My bad. Went to take more measurements. The bottom plastic strips are fine, it's the top strip that is damaged. But it appears I can convert to an external overflow box easier than I thought.
I can take the top strips off, remove the internal horizontal glass runners, then add 3/4" x 3" strips to top "euro" brace the front and two sides. Add an overflow box on the back and let it flow over the back. This should give me 65-66" linear overflow 3/4" high. Might have to add 3/8" to trip the inside opening of the "euro" bracing to raise the sides of the weir?
Make the bottom of the overflow box 3/4" thick so it's the horizontal back brace? One inch for extra safety?